Mobile Ad hoc Networks Working Group C. Perkins
Internet-Draft Futurewei
Intended status: Standards Track S. Ratliff
Expires: September 25, 2015 Idirect
J. Dowdell
Airbus Defence and Space
L. Steenbrink
HAW Hamburg, Dept. Informatik
V. Mercieca
Airbus Defence and Space
March 24, 2015

Dynamic MANET On-demand (AODVv2) Routing
draft-ietf-manet-aodvv2-08

Abstract

The revised Ad Hoc On-demand Distance Vector (AODVv2) routing protocol is intended for use by mobile routers in wireless, multihop networks. AODVv2 determines unicast routes among AODVv2 routers within the network in an on-demand fashion, offering rapid convergence in dynamic topologies.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on September 25, 2015.

Copyright Notice

Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

1. Overview

The revised Ad Hoc On-demand Distance Vector (AODVv2) routing protocol [formerly named DYMO] enables on-demand, multihop unicast routing among AODVv2 routers in mobile ad hoc networks [MANETs][RFC2501]. The basic operations of the AODVv2 protocol are route discovery and route maintenance. Route discovery is performed when an AODVv2 router must transmit a packet towards a destination for which it does not have a route. Route maintenance is performed to avoid prematurely expunging routes from the route table, and to avoid dropping packets when a route breaks.

During route discovery, the originating AODVv2 router (RREQ_Gen) disseminates a Route Request message (RREQ) to find a route toward some target destination. Using a hop-by-hop regeneration algorithm, each AODVv2 router receiving the RREQ message records a route toward the originator. When the target's AODVv2 router (RREP_Gen) receives the RREQ, it records a route toward RREQ_Gen and generates a Route Reply (RREP) unicast toward RREQ_Gen. Each AODVv2 router that receives the RREP stores a route toward the target, and again unicasts the RREP toward the originator. When RREQ_Gen receives the RREP, routes have then been established between RREQ_Gen (the originating AODVv2 router) and RREP_Gen (the target's AODVv2 router) in both directions.

Route maintenance consists of two operations: continuously extending the lifetime of active routes, and using Route Error (RERR) message to invalidate routes that cannot be used to forward packets. In order to maintain routes, AODVv2 routers extend route lifetimes upon successfully forwarding a packet. When a data packet is received to be forwarded and no valid route exists, then the upstream routers and AODVv2 router of the source of the packet is notified of the error by way of an RERR message. Route discovery would re-establish the route. RERR messages are also used to notify upstream routers when routes break (say, due to loss of a link to a neighbor).

AODVv2 uses sequence numbers to assure loop freedom [Perkins99], similarly to AODV. Sequence numbers enable AODVv2 routers to determine the temporal order of AODVv2 route discovery messages, thereby avoiding use of stale routing information.

See Section 10 for the mapping of AODVv2 data elements to RFC 5444 Address Block, Address TLV, and Message TLV formats. Security for authentication of AODVv2 routers, and/or encryption of traffic is dealt with by the underlying transport mechanism (e.g., by using the techniques for Authentication, Integrity, and Confidentiality documented in [RFC5444]).

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. In addition, this document uses terminology from [RFC5444], and defines the following terms:

Adjacency

A bi-directional relationship between neighboring AODVv2 routers for the purpose of exchanging routing information. Not every pair of neighboring routers will necessarily form an adjacency. Monitoring of adjacencies where packets are being forwarded is required (see Section 6.2).
AckReq

Request for acknowledgement (of an RREP message).
AODVv2 Router

An IP addressable device in the ad-hoc network that performs the AODVv2 protocol operations specified in this document.
Current_Time

The current time as maintained by the AODVv2 router.
Data Element

A named object used within AODVv2 protocol messages
Disregard

Ignore for further processing.
Handling Router (HandlingRtr)

HandlingRtr denotes the AODVv2 router receiving and handling an AODVv2 message.
Invalid route

A route that cannot be used for forwarding.
MANET

A Mobile Ad Hoc Network as defined in [RFC2501].
MetricList

The metrics associated with the addresses in an AddressList.
Node

An IP addressable device in the ad-hoc network. A node may be an AODVv2 router, or it may be a device in the network that does not perform any AODVv2 protocol operations. All nodes in this document are either AODVv2 Routers or else Router Clients.
OrigAddr

An IP address of the Originating Node used as a data element within AODVv2 messages.
OrigAddrMetric

The metric associated with the route to OrigAddr.
OrigSeqNum

The Sequence Number maintained by OrigNode for OrigAddr.
Originating Node (OrigNode)

The Originating Node is the node that launched the application requiring communication with the Target Address. If OrigNode is a Router Client, its AODVv2 router (RREQ_Gen) has the responsibility to generate a AODVv2 RREQ message on behalf of OrigNode as necessary to discover a route.
PktSource

The source address of a packet sent to an unreachable address.
PrefixLengthList

The prefix lengths associated with addresses in an AddressList.
Reactive

A protocol operation is called "reactive" if it is performed only in reaction to specific events. As used in this document, "reactive" is synonymous with "on-demand".
Routable Unicast IP Address

A routable unicast IP address is a unicast IP address that is scoped sufficiently to be forwarded by a router. Globally-scoped unicast IP addresses and Unique Local Addresses (ULAs).[RFC4193] are examples of routable unicast IP addresses.
Route Error (RERR)

A RERR message is used to indicate that an AODVv2 router does not have a route toward one or more particular destinations.
Route Reply (RREP)

A RREP message is used to establish a route between the Target Address and the Originating Address, at all the AODVv2 routers between them.
Route Request (RREQ)

An AODVv2 router uses a RREQ message to discover a valid route to a particular destination address, called the Target Address. An AODVv2 router processing a RREQ receives routing information for the Originating Address.
Router Client

A node that requires the services of an AODVv2 router for route discovery and maintenance. An AODVv2 router is always its own client, so that its list of client IP addresses is never empty.
Router Interface

An interface supporting the transmission or reception of Router Messages.
RREP Generating Router (RREP_Gen)

The RREP Generating Router is the AODVv2 router that serves TargNode. RREP_Gen generates the RREP message to advertise a route towards TargAddr from OrigAddr.
RREQ Generating Router (RREQ_Gen)

The RREQ Generating Router is the AODVv2 router that serves OrigNode. RREQ_Gen generates the RREQ message to discover a route for TargAddr.
Sequence Number (SeqNum)

A Sequence Number is an unsigned integer maintained by an AODVv2 router to avoid re-use of stale messages. The router associates SeqNum with an IP address of one or more of its network interfaces. The value zero (0) is reserved to indicate that the Sequence Number for an address is unknown.
SeqNumList

The list of Sequence Numbers associated with addresses in an AddressList, used in RERR messages.
TargAddr

An IP address of the Target Node used as a data element within AODVv2 messages.
TargAddrMetric

The metric associated with the route to TargAddr.
TargSeqNum

The Sequence Number maintained by TargNode for TargAddr.
Target Node (TargNode)

The node hosting the IP address towards which a route is needed.
Type-Length-Value structure (TLV)

A generic way to represent information, for example as used in [RFC5444].
Unreachable Address

An address for which a valid route is not known.
upstream

In the direction from TargAddr to OrigAddr.
Valid route

A route that can be used for forwarding.
ValidityTime

The duration of time for which a route should be considered to be a valid route.





















3. Data Elements and Notational Conventions

This document uses the Data Elements and conventions found in Table 1 and Table 2.

Data Elements Meaning
msg_hop_limit Number of hops allowable for the message
msg_hop_count Number of hops traversed so far by the message
AckReq Acknowledgement Requested for RREP
PktSource Source address of a data packet
AddressList A list of IP addresses
OrigAddr IP address of the Originating Node
TargAddr IP address of the Target Node
UnreachableAddress An unreachable IP address
PrefixLengthList Routing prefixes associated with addresses in AddressList
SeqNum Sequence Number, used in RERR messages
SeqNumList A list of SeqNums
OrigSeqNum Originating Node Sequence Number
TargSeqNum Target Node Sequence Number
MetricType The metric type for values in MetricList
MetricList Metric values for routes to addresses in AddressList
OrigAddrMetric Metric value for route to OrigAddr
TargAddrMetric Metric value for route to TargAddr
ValidityTime Included in ValidityTimeList
ValidityTimeList ValidityTime values for routes to Addresses in AddressList
Notation Meaning
Route[Address] A route table entry towards Address
Route[Address].{field} A field in such a route table entry
-- --
RREQ_Gen AODVv2 router originating an RREQ
RREP_Gen AODVv2 router responding to an RREQ
RERR_Gen AODVv2 router originating an RERR
RteMsg Either RREQ or RREP
RteMsg.{field} Field in RREQ or RREP
AdvRte A route advertised in an incoming RteMsg
HandlingRtr Handling Router

4. Applicability Statement

The AODVv2 routing protocol is a reactive routing protocol designed for stub (i.e., non-transit) or disconnected (i.e., from the Internet) mobile ad hoc networks (MANETs). AODVv2 handles a wide variety of mobility patterns by determining routes on-demand. AODVv2 also handles a wide variety of traffic patterns. In networks with a large number of routers, AODVv2 is best suited for relatively sparse traffic scenarios where any particular router forwards packets to only a small percentage of the AODVv2 routers in the network, due to the on-demand nature of route discovery and route maintenance. AODVv2 supports routers with multiple interfaces, as long as each interface has its own (unicast routeable) IP address; the set of all network interfaces supporting AODVv2 is administratively configured in a list (namely, AODVv2_INTERFACES).

Ad Hoc networks have been deployed in many circumstances, including for emergency and disaster relief. In those circumstances, it is sometimes the case that the simple ability to communicate is much more important than being assured of secure operations. AODVv2 is very well suited for such reactive scenarios. For other ad hoc networking applications, in which insecure operation could negate the value of establishing communication paths, it is important for neighboring AODVv2 nodes to establish security associations with one another.

Although AODVv2 is closely related to AODV [RFC3561], and shares some features of DSR [RFC4728], AODVv2 is not interoperable with either of those other two protocols.

AODVv2 is applicable to memory constrained devices, since only a little routing state is maintained in each AODVv2 router. Routes that are not needed for forwarding data do not have to be maintained, in contrast to proactive routing protocols that require routing information to all routers within the MANET be maintained.

In addition to routing for its own local applications, each AODVv2 router can also route on behalf of other non-routing nodes (in this document, "Router Clients") that are directly reachable via its network interfaces. Each AODVv2 router, if serving router clients other than itself, SHOULD be configured with information about the IP addresses of its clients, using any suitable method. In the initial state, no AODVv2 router is required to have information about the relationship between any other AODVv2 router and its Router Clients (see Section 6.3).

The coordination among multiple AODVv2 routers to distribute routing information correctly for a shared address (i.e. an address that is advertised and can be reached via multiple AODVv2 routers) is not described in this document. The AODVv2 router operation of shifting responsibility for a routing client from one AODVv2 router to another is described in Appendix I. Address assignment procedures are entirely out of scope for AODVv2. A Router Client SHOULD NOT be served by more than one AODVv2 router at any one time.

AODVv2 routers perform route discovery to find a route toward a particular destination. AODVv2 routers MUST must be configured to respond to RREQs for themselves and their clients. When AODVv2 is the only protocol interacting with the forwarding table, AODVv2 MAY be configured to perform route discovery for all unknown unicast destinations. Such routers will reply for each address request.

By default, AODVv2 only supports bidirectional links. In the case of possible unidirectional links, blacklists (see Section 6.2) SHOULD be used, or other means (e.g. adjacency establishment with only neighboring routers that have bidirectional communication as indicated by NHDP HELLO messages [RFC6130]) of assuring and monitoring bi-directionality are recommended. Otherwise, persistent packet loss or persistent protocol failures could occur. If received over a link that is unidirectional, metric information from incoming AODVv2 messages MUST NOT be used for route table updates.

The routing algorithm in AODVv2 may be operated at layers other than the network layer, using layer-appropriate addresses. The routing algorithm makes use of some persistent state; if there is no persistent storage available for this state, recovery can impose a performance penalty (e.g., in case of AODVv2 router reboots).

5. AODVv2 Message Transmission

In its default mode of operation, AODVv2 sends messages using the parameters for port number and IP protocol specified in [RFC5498]. Unless otherwise specified, the address for AODVv2 multicast messages (for example, RREQ or RERR) is the link-local multicast address LL-MANET-Routers [RFC5498]. All AODVv2 routers MUST subscribe to LL-MANET-Routers [RFC5498] to receive AODVv2 messages. Implementations are free to choose their own heuristics for reducing multicast overhead. Some methods for doing so are described in [RFC6621]. AODVv2 does not specify which method should be used to restrict the set of AODVv2 routers that have the responsibility to regenerate multicast packets. Note that multicast packets MAY be sent via unicast. For example, this may occur for certain link-types (non-broadcast media), for manually configured router adjacencies, or in order to improve robustness.

When multiple interfaces are available, a node transmitting a multicast packet to LL-MANET-Routers MUST send the packet on all interfaces that have been configured for AODVv2 operation. Similarly, AODVv2 routers MUST subscribe to LL-MANET-Routers on all their AODVv2 interfaces.

IP packets containing AODVv2 protocol messages SHOULD be given priority queuing and channel access.

6. Data Structures

6.1. Route Table Entry

The route table entry is a conceptual data structure. Implementations MAY use any internal representation so long as it provides access to the information specified below.

A route table entry has the following fields:

Route.Address

An address or address prefix of a node
Route.PrefixLength

The length of the address or prefix. If the value of Route.PrefixLength is less than the length of Route.Address, the route can be thought of as a route to the subnet on which Route.Address resides. A PrefixLength is stored for every route in the route table.
Route.SeqNum

The Sequence Number associated with Route.Address, as obtained from the last packet that successfully updated this route table entry.
Route.NextHop

The IP address of the adjacent AODVv2 router used for the path toward the Route.Address
Route.NextHopInterface

The interface used to send packets toward Route.Address
Route.LastUsed

The time that this route was last used to forward a packet
Route.LastSeqNum

The time that the destination SeqNum for this route was last updated
Route.ExpirationTime

The time at which this route must be marked as Invalid
Route.MetricType

The type of the metric for the route towards Route.Address
Route.Metric

The cost of the route towards Route.Address expressed in units consistent with Route.MetricType
Route.State

The last *known* state (one of Active, Idle, or Invalid) of the route
Route.Timed

TRUE if the route was specified to have a ValidityTime
Route.Precursors (optional)

A list of upstream neighbors using the route (see Section 12.2)

A route table entry (i.e., a route) is in one of the following states:

Active

An Active route is in current use for forwarding packets. An Active route is maintained continuously by AODVv2 and is considered to remain active as long as it is used at least once during every ACTIVE_INTERVAL, or if the Route.Timed flag is true. When a route that is not a timed route is no longer active the route becomes an Idle route.
Idle

An Idle route can be used for forwarding packets, even though it is not in current use. If an Idle route is used to forward a packet, it becomes an Active route once again. After an Idle route remains idle for MAX_IDLETIME, it becomes an Invalid route.
Invalid

A route marked as Invalid cannot be used for forwarding, but the sequence number information MAY be maintained until the destination sequence number has not had any updates for MAX_SEQNUM_LIFETIME; after that time, old sequence number information may no longer be valid and the Invalid route MUST be expunged.

MAX_SEQNUM_LIFETIME is the time after a reboot during which an AODVv2 router MUST NOT respond to any routing messages that require information about its Sequence Number. Thus, if all other AODVv2 routers expunge routes to the rebooted router after that time interval, the rebooted AODVv2 router's sequence number will not be considered stale by any other AODVv2 router in the MANET.

The invalidation of a Timed route is controlled by the ExpirationTime time of the route table entry (instead of MAX_IDLETIME). Until that time, a Timed route can be used for forwarding packets. A route is indicated to be a Timed route by the setting of the Timed flag in the route table entry. Afterwards, the route MAY be expunged; otherwise the route must be must be marked as Invalid.

6.2. Next-hop Router Adjacency Monitoring and Blacklists

Neighboring routers MAY form an adjacency based on AODVv2 messages, other protocols (e.g. NDP [RFC4861] or NHDP [RFC6130]), or manual configuration. Loss of a routing adjacency may also be indicated similarly. AODVv2 routers SHOULD monitor connectivity to adjacent routers along active routes. In the absence of other information about bidirectional connectivity, the default approach for AODVv2 routers to monitor connectivity to neighboring AODVv2 routers is to include the AckReq data element in RREP messages, and send RREP_Ack messages to fulfill the requests (see Sections 9.2 and 9.4). However, when routers perform other operations such as those from the list below, these can also be used as indications of connectivity.

  • NHDP HELLO Messages [RFC6130], if is implemented by its neighbors
  • Route timeout
  • Lower layer triggers, e.g. message reception or link status notifications
  • TCP timeouts
  • Promiscuous listening
  • Other monitoring mechanisms or heuristics

For example, receipt of a Neighborhood Discovery message would signal a connection to the sender. In this case, the AODVv2 router doesn't need to request an acknowledgement in the RREP. Similarly, if AODVv2 received notification of a timeout, this may possibly be due to a disconnection, and the AODVv2 router SHOULD attempt to verify connectivity by including AckReq data element when sending a RREP to that neighbor.

When a link to a neighbor is determined to be unidirectional, either by failure to respond with a RREP_Ack as requested, or by some other means, the neighbor MUST be placed in a blacklist. However, the blacklisted neighbor SHOULD NOT be permanently blacklisted; after a certain time (MAX_BLACKLIST_TIME), it SHOULD once again be considered as a viable neighbor for route discovery operations.

For this purpose, a list of blacklisted routers along with their time of removal SHOULD be maintained:

Blacklist.Router

An IP address of the router that did not verify bidirectional connectivity
Blacklist.RemoveTime

The time at which Blacklist.Router SHOULD be removed from the blacklist

RREQs received from a blacklisted router, or any router over a link that is known to be incoming-only, MUST be disregarded. If other indications are received that a blacklisted router has restored bidirectional connectivity, for instance receiving NHDP HELLO messages, then the router SHOULD be immediately removed from the blacklist.

6.3. Router Clients and Client Networks

An AODVv2 router may offer routing services to other nodes that are not AODVv2 routers; such nodes are called Router Clients in this document.

For this purpose, CLIENT_ADDRESSES must be configured on each AODVv2 router with the following information:

Client IP address

The IP address of the node that requires routing service from the AODVv2 router.
Client Prefix Length

The length of the routing prefix associated with the client IP address.

The list of Routing Clients for an AODVv2 router is never empty, since an AODVv2 router is always its own client as well. If the Client Prefix Length is not the full length of the Client IP address, then the prefix defines a Client Network. If an AODVv2 router is configured to serve a Client Network, then the AODVv2 router MUST serve every node that has an address within the range defined by the routing prefix of the Client Network.

6.4. Sequence Numbers

Sequence Numbers allow AODVv2 routers to evaluate the freshness of routing information. Each AODVv2 router in the network MUST maintain its own sequence number (SeqNum). Each RREQ and RREP generated by an AODVv2 router includes its SeqNum. Each AODVv2 router MUST ensure that its SeqNum is monotonically increasing. The router can ensure this by incrementing SeqNum whenever it generates RREQ or RREP .

A router receiving a RREQ or RREP message uses the Sequence Number in the message to determine the freshness of a route update: if a new Sequence Number in the message is lower than the one stored in the route table, the stored information for that route is considered stale.

As a consequence, loop freedom is assured.

If the router has multiple network interfaces, it can use the same SeqNum for the IP addresses of all of them, or it can assign different SeqNums for use with different IP addresses. However, the router MUST NOT use multiple SeqNums for any particular IP address. A Router Client has the same SeqNum as the IP address of the network interface that the AODVv2 router uses to forward packets to that Router Client. Similarly, a route to a subnet has the same SeqNum as the IP address of the network interface that the AODVv2 router uses to forward packets to that subnet. The Sequence Number fulfills the same role as the "Destination Sequence Number" of DSDV [Perkins94], and as the AODV Sequence Number in RFC 3561[RFC3561].

An AODVv2 router increments its SeqNum as follows. Most of the time, SeqNum is incremented by simply adding one (1). But when the SeqNum has the value of the largest possible number representable as a 16-bit unsigned integer (i.e., 65,535), it MUST be incremented by setting to one (1). In other words, the sequence number after 65,535 is 1.

An AODVv2 router SHOULD maintain its SeqNum in persistent storage. If an AODVv2 router's SeqNum is lost, it MUST take the following actions to avoid the danger of routing loops. First, the AODVv2 router MUST set Route.State := Invalid for each entry. Furthermore the AODVv2 router MUST wait for at least MAX_SEQNUM_LIFETIME before transmitting or regenerating any AODVv2 RREQ or RREP messages. If an AODVv2 protocol message is received during this waiting period, the AODVv2 router SHOULD perform normal route table entry updates, but not forward the message to other nodes. If, during this waiting period, a data packet is received to be forwarded to another destination that is not among the router's Clients, then the AODVv2 router MUST transmit a RERR message indicating that no route is available. However, packets destined to a Client are forwarded as usual. At the end of the waiting period the AODVv2 router sets its SeqNum to one (1) and begins performing AODVv2 protocol operations again.

6.5. Table for Multicast RteMsgs

Two multicast RteMsgs (i.e., RREQ or RREP) are considered to be "comparable" if they have the same Message Type, OrigAddr, TargAddr, and MetricType. When RteMsgs are flooded in a MANET, an AODVv2 router may well receive such comparable RteMsgs from its neighbors. A router, after receiving a RteMsg, MUST check against previous RteMsgs to assure that its response message would contain information that is not redundant. Otherwise, multicast RteMsgs are likely to be regenerated repeatedly with almost no additional benefit, but generating a great deal of unnecessary signaling traffic and interference. See Section 8.6 regarding suppression of redundant RteMsgs.

To avoid transmission of redundant RteMsgs, while still enabling the proper handling of earlier RteMsgs that may have somehow been delayed in the network, each AODVv2 router keeps a list of certain information about recently received RteMsgs. This list is called the AODVv2 Multicast RteMsg Table -- or, more briefly, the RteMsg Table.

Each entry in the RteMsg Table has the following fields:

  • Message Type (either RREQ or RREP)
  • OrigAddr
  • TargAddr
  • OrigSeqNum (if present)
  • TargSeqNum (if present)
  • MetricType
  • Timestamp (Current_Time at the time the entry is updated)

The RteMsg Table is maintained so that no two entries in the RteMsg Table are comparable -- that is, all RteMsgs represented in the RteMsg Table either have different Message Types, different OrigAddr, different TargAddr, or different metric types. If two RteMsgs have the same Message Type, MetricType, OrigAddr, and TargAddr, the information from the one with the older Sequence Number is not needed in the table; in case they have the same Sequence Number, the one with the greater Metric value is not needed; in case they have the same Metric as well, it does not matter which table entry is maintained. Whenever a RteMsg Table entry is updated, its Timestamp field MUST also set to be the Current_Time.

7. Metrics

Metrics measure a cost or quality associated to a route or a link. They can account for various characteristics such as latency, delay, financial, energy, etc. A metric value is included in each routing table entry. Determining whether to use incoming information about a route requires comparing metric values. Whenever an AODV router receives metric information in an incoming message, the received value of the metric is as measured by the neighbor router, and does not reflect the cost of traversing the link to that neighbor.

Each metric has a MetricType, which is allocated by IANA as specified in [RFC6551]. Apart from its default metric type as detailed in Section 7.3, AODVv2 enables the use of monotonically increasing metrics, whose data type depends on the metric used. Using non-default metrics in a RteMsg requires the inclusion of the MetricType data element. Routes are looked up according to metric type, and intermediate routers handling a RteMsg assign the same metric type to all metric information in the RteMsg.

For each type of metric, a maximum value is defined, denoted MAX_METRIC[i] where 'i' is the MetricType. AODVv2 cannot store routes in its route table that cost more than MAX_METRIC[i].

7.1. The Cost() function

In order to simplify the description of storing accumulated route costs in the route table, a Cost() function is defined. This function returns the Cost of traversing a Route ('Cost(R)') or a Link ('Cost(L)'). Cost(L) for DEFAULT_METRIC_TYPE is specified in Section 7.3. The Cost() function for other metrics is beyond the scope of this document.

7.2. The LoopFree() function

Since determining loop freedom is known to depend on comparing the Cost(R1) of advertised route update information to the Cost(R2) of an existing stored route using the same metric type, AODVv2 invokes a function called "LoopFree(R1, R2)". LoopFree(R1, R2) returns TRUE when R1 is guaranteed to not rely on the route R2, i.e. R2 is not a subroute of the route R1. An AODVv2 router invokes LoopFree() to compare an advertised route to a stored route. The advertised route is referred to as AdvRte and is used as parameter R1. The stored route is referred to as Route and is used as parameter R2.

7.3. Default Metric type

The default MetricType (DEFAULT_METRIC_TYPE) is HopCount (but see Section 7.4). HopCount is the only metric described in detail in this document. For the HopCount metric, Cost(L) is always 1, and Cost(R) is the hop count between the router and the destination.

MAX_METRIC[DEFAULT_METRIC_TYPE] is defined to be MAX_HOPCOUNT. MAX_HOPCOUNT MUST be larger than the AODVv2 network diameter. Otherwise, AODVv2 protocol messages may not reach their intended destinations.

Using MetricType DEFAULT_METRIC_TYPE, LoopFree (AdvRte, Route) is TRUE when Cost(AdvRte) ≤ Cost(Route). The specification of Cost(R) and LoopFree(AdvRte, Route) for metric types other than DEFAULT_METRIC_TYPE is beyond the scope of this document.

7.4. Alternate Metrics

Some applications may require metric information other than HopCount, which has traditionally been the default metric associated with routes in MANET. It is well known that reliance on HopCount can cause selection of the worst possible route in some situations. For this reason, AODVv2 enables route selection based on metric information other than HopCount -- in other words, based on "alternate metrics".

The range and data type of each such alternate metric may be different. For instance, the data type might be integers, or floating point numbers, or restricted subsets thereof. It is out of the scope of this document to specify for alternate metrics the Cost(L) and Cost(R) functions, or their return type. Where necessary these should take into account any differences in the link cost in each direction.

8. AODVv2 Protocol Operations

In this section, operations are specified for updating the route table using information within AODVv2 RteMsgs (either RREQ or RREP), and due to timeouts. AdvRte is the route advertised by the RteMsg. RteMsgs include IP addresses as well as possibly the SeqNum and the prefix lengths associated with those IP addresses. The AdvRte also includes the metric measured from the neighbor transmitting the RteMsg to the IP address originating the route update. All SeqNum comparisons use signed 16-bit arithmetic.

8.1. Evaluating Incoming Routing Information

After determining that the incoming information is correctly formatted and contains values in the correct ranges, the AODVv2 router will use the information to update local routing information if possible. This section explains how to determine whether the incoming information should be used to update the route table, and how to perform the update.

The incoming RteMsg may be a RREQ or a RREP. If it is a RREQ, it contains information about a route to OrigAddr. Prefix length information in a RREQ, if present, describes the subnet on which OrigAddr resides. If it is a RREP, it contains information about a route to TargAddr. AdvRte is used to denote the route information contained in the RteMsg. AdvRte has the following properties: Section 8.2. Otherwise determine whether or not to use AdvRte for updating the route entry (Route) matching the AdvRte's Address and MetricType as follows: Appendix A.1.1.

  • AdvRte.Address = OrigAddr (in RREQ) or TargAddr (in RREP).
  • AdvRte.SeqNum = OrigSeqNum (in RREQ) or TargSeqNum (in RREP).
  • AdvRte.MetricType = RteMsg.MetricType, if present, else DEFAULT_METRIC_TYPE.
  • AdvRte.Metric = RteMsg.Metric.
  • AdvRte.Cost = AdvRte.Metric + Cost(L) according to the indicated MetricType, where L is the link from the advertising router.
  • AdvRte.ValidityTime = ValidityTime in the RteMsg, if present.

In the description below, Route denotes the stored routing table entry and HandlingRtr is the router receiving the RteMsg. HandlingRtr MUST process the incoming information as follows. If the routing table does not contain an entry matching AdvRte's Address and MetricType, create a new route table entry according to the procedure in

  1. Check whether AdvRte is stale (AdvRte.SeqNum < Route.SeqNum).
    • If AdvRte's sequence number is newer, HandlingRtr MUST use AdvRte to update the Route.
    • If stale, using the incoming information might result in a routing loops. In this case the HandlingRtr MUST NOT use AdvRte to update the Route.
    • If the SeqNums are equal, continue checking as below.
  2. Check whether AdvRte advertises a more costly route (AdvRte.Cost >= Route.Metric).
    • If the advertised route's cost is the same or greater than the stored route, and the stored route is valid, the incoming information does not offer any improvement and SHOULD NOT be used to update the stored route table entry.
    • If the advertised route's cost is lower than the stored route, AdvRte offers improvement and SHOULD be used to update the stored route table entry.
    • If the advertised route's cost is the same or greater than the stored route, but the stored route's state is Invalid, continue processing to see whether there is a danger of a routing loop.
  3. Check whether the information is safe against loops (LoopFree (AdvRte, Route) == TRUE).
    • If LoopFree (see Section 7.2) returns false, using the incoming information might cause a routing loop. AdvRte MUST NOT be used to update the stored route table entry.
  4. If the advertised route can be used to update the route table entry, follow the procedure in Section 8.2.

To briefly summarize, AdvRte must satisfy the following conditions compared to the existing route table entry before it can be used:

  • AdvRte is more recent, (i.e., AdvRte.SeqNum > Route.SeqNum) OR
  • AdvRte is not stale and can safely restore an invalid route (i.e. LoopFree (AdvRte, Route) == TRUE), OR
  • AdvRte is not stale and is less costly.

Also see the pseudocode in

If the route has been updated based on information in a received RREQ, the AODVv2 router MAY force regeneration of the RREQ, to ensure the most recent information is propagated to other routers, but it MAY suppress this to avoid extra control traffic.

8.2. Applying Route Updates To Route Table Entries

To apply the route update, a route table entry for AdvRte.Address is either found to already exist in the route table, or else a new route table entry for AdvRte.Address is created and inserted into the route table. If the route table entry had to be created, or if the state is Invalid, the state is set to be Idle. The fields of route table entry are assigned as follows:

  • If AdvRte.PrefixLength exists, then Route.PrefixLength := AdvRte.PrefixLength. Otherwise, Route.PrefixLength := maximum length for address family (either 32 or 128).
  • Route.SeqNum := AdvRte.SeqNum
  • Route.NextHop := IP.SourceAddress (i.e., the address from which the RteMsg was received)
  • Route.NextHopInterface is set to the interface on which RteMsg was received
  • Route.MetricType := AdvRte.MetricType
  • Route.Metric := AdvRte.Cost
  • Route.LastUsed := Current_Time
  • Route.LastSeqnum := Current_Time
  • If RteMsg.ValidityTime is included, then
    Route.ExpirationTime := Current_Time + RteMsg.ValidityTime and Route.Timed := TRUE. Otherwise, Route.Timed := FALSE and Route.ExpirationTime := MAXTIME.

With these assignments to the route table entry, a route has been made available, and the route can be used to send any buffered data packets (and subsequently to forward any incoming data packets) for Route.Address. An updated route entry also fulfills any outstanding route discovery (RREQ) attempts for Route.Address. Any retry timers for the RREQ SHOULD be cancelled.

8.3. Route Maintenance

AODVv2 routers attempt to maintain active routes. Before using a route to forward a packet, an AODVv2 router MUST check the status of the route as specified in Section 8.4. If the route has been marked as Invalid, it cannot be used for forwarding. Otherwise, set Route.LastUsed := Current_Time, Route.State := Active, and forward the packet to the route's next hop.

When a routing problem is encountered, an AODVv2 router (denoted RERR_Gen) sends the RERR to quickly notify upstream routers. Two kinds of routing problems can trigger generation of a RERR message. The first happens when the router receives a packet but does not have a valid route for the destination of the packet. The second case happens immediately upon detection of a broken link (see Section 6.2) for an valid route.

Optionally, if a precursor list is maintained for the route, see Section 12.2 for precursor lifetime operations.

8.4. Route Table Entry Timeouts

During normal operation, AODVv2 does not require any explicit timeouts to manage the lifetime of a route. At any time, any route table entry can be examined and then either expunged or marked as Invalid according to the following rules.

The following rules are used to manage the state of route table entries: Section 12.2) then the precursor lists must also be expunged at the same time that the route itself is expunged.

  • If Current_Time > Route.ExpirationTime, set Route.State := Invalid.
  • If (Current_Time - Route.LastUsed) > (ACTIVE_INTERVAL + MAX_IDLETIME), and if (Route.Timed == FALSE), set Route.State := Invalid.
  • If (Current_Time - Route.LastUsed) > ACTIVE_INTERVAL, and if (Route.Timed == FALSE), set Route.State := Idle.
  • If (Current_Time - Route.LastSeqNum > MAX_SEQNUM_LIFETIME), and the route is Invalid, the route table entry MUST be expunged. If the route is not invalid and MAX_SEQNUM_LIFETIME has expired, the SeqNum information should be removed from the route, to avoid problems with boot sequence and lost SeqNum behaviour.

Memory constrained devices MAY choose to expunge routes from the AODVv2 route table at other times, but MUST adhere to the following rules:

  • An Active route MUST NOT be expunged.
  • An Idle route SHOULD NOT be expunged.
  • Any Invalid route MAY be expunged; least recently used Invalid routes SHOULD be expunged first.

If precursor lists are maintained for the route (as described in

8.5. Route Discovery, Retries and Buffering

AODVv2 message types RREQ and RREP are together known as Routing Messages (RteMsgs) and are used to discover a route between an Originating and Target Address, denoted by OrigAddr and TargAddr. The constructed route is bidirectional, enabling packets to flow between OrigAddr and TargAddr. RREQ and RREP have similar information and function, but have some differences in their rules for handling. When a node receives a RREQ or a RREP, the node then creates or updates a route to the OrigAddr or the TargAddr respectively (see Section 8.1). The main difference between the two messages is that, by default, RREQ messages are multicast to solicit a RREP, whereas RREP is unicast as a response to RREQ.

When an AODVv2 router needs to forward a data packet from a node (with IP address OrigAddr) in its set of router clients, and it does not have a forwarding route toward the packet's IP destination address (TargAddr), the AODVv2 router (RREQ_Gen) generates a RREQ (as described in Section 9.1.1) to discover a route toward TargAddr. Subsequently RREQ_Gen awaits reception of an RREP message (see Section 9.2.1) or other route table update (see Section 8.2) to establish a route toward TargAddr. The RREQ message contains routing information to enable RREQ recipients to route packets one hop towards the OrigAddr, and the RREP message contains routing information to enable RREP recipients to route packets one hop towards the TargAddr.

After issuing a RREQ, as described above RREQ_Gen awaits a RREP providing a bidirectional route toward the Target Address. If the RREP is not received within RREQ_WAIT_TIME, RREQ_Gen MAY retry the Route Discovery by generating another RREQ. Route Discovery SHOULD be considered to have failed after DISCOVERY_ATTEMPTS_MAX and the corresponding wait time for a RREP response to the final RREQ. After the attempted Route Discovery has failed, RREQ_Gen MUST wait at least RREQ_HOLDDOWN_TIME before attempting another Route Discovery to the same destination.

To reduce congestion in a network, repeated attempts at route discovery for a particular Target Address SHOULD utilize a binary exponential backoff, as described in [RFC3561], where the initial wait time is RREQ_WAIT_TIME and the wait time is doubled for each retry based.

Data packets awaiting a route SHOULD be buffered by RREQ_Gen. This buffer SHOULD have a fixed limited size (BUFFER_SIZE_PACKETS or BUFFER_SIZE_BYTES). Determining which packets to discard first is a matter of policy at each AODVv2 router; in the absence of policy constraints, by default older data packets SHOULD be discarded first. Buffering of data packets can have both positive and negative effects (albeit usually positive). Nodes without sufficient memory available for buffering SHOULD be configured to disable buffering by configuring BUFFER_SIZE_PACKETS = 0 and BUFFER_SIZE_BYTES = 0. This will affect the latency required for launching TCP applications to new destinations.

If a route discovery attempt has failed (i.e., DISCOVERY_ATTEMPTS_MAX attempts have been made without receiving a RREP) to find a route toward the Target Address, any data packets buffered for the corresponding Target Address MUST BE dropped and a Destination Unreachable ICMP message (Type 3) SHOULD be delivered to the source of the data packet. The code for the ICMP message is 1 (Host unreachable error). If RREQ_Gen is not the source (OrigNode), then the ICMP is sent to OrigAddr.

8.6. Suppressing Redundant RteMsgs

When RREQ messages are flooded in a MANET, an AODVv2 router may receive similar RREQ messages from more than one of its neighbours. To avoid processing and transmission associated with redundant RteMsgs, while still enabling proper handling of earlier RteMsgs that may have somehow been delayed in the network, it is necessary for each AODVv2 router store information about RteMsgs which it has recently received (see the RteMsg table defined in Section 6.5).

When a RREQ is received, it is checked against the RteMsg Table to see if it contains redundant information. If so it does not need to be processed.

For RREQ messages, the process for comparison is as follows:

  • Look for a "comparable" entry in the RteMsg Table with the same MsgType, OrigAddr, TargAddr, and MetricType.
  • If there is none, create an entry to store information about the received RREQ, and continue to regenerate the RREQ.
  • If there is an entry, and it has a lower SeqNum for OrigAddr than the received RREQ, update it using the new RREQ and continue to regenerate the RREQ.
  • If there is an entry and it has a higher SeqNum for OrigAddr than the received RREQ, do not replace the entry and do not process the RREQ.
  • If there is an entry and it has the same SeqNum for OrigAddr and a higher Metric than the received RREQ, update it with the new RREQ information.
  • If there is an entry and it has the same SeqNum for OrigAddr and a Metric less than or equal to the received RREQ, do not replace the entry and do not regenerate the RREQ.
  • In all cases, update the timestamp field, since other comparable RREQs may still be traversing the network.

The process of comparison for optional multicast RREP messages is analogous, substituting RREP for RREQ, and TargAddr for OrigAddr. Entries in the RteMsg Table MUST be deleted after MAX_SEQNUM_LIFETIME, but should be maintained for at least RteMsg_ENTRY_TIME in order to account for long-lived RREQs traversing the network.

9. AODVv2 Protocol Messages

This section specifies the data elements and values required in AODVv2 protocol messages, namely RREQ, RREP, RERR, and RREP_Ack.

To avoid congestion, each AODVv2 router's rate of packet/message generation SHOULD be limited. The rate and algorithm for limiting messages (CONTROL_TRAFFIC_LIMIT) is left to the implementor and should be administratively configurable. AODVv2 messages SHOULD be discarded in the following order of preference: RREQ, RREP, RERR, and finally RREP_Ack.

See Section 10 for the mapping of AODVv2 data elements to RFC 5444 Message TLVs, Address Blocks, and Address TLVs.

9.1. RREQ Messages

RREQ messages are used in Route Discovery operations to request a route to a specified Target address. RREQ messages have the following general structure:

  +-----------------------------------------------------------------+
  |                   msg_hop_limit, msg_hop_count                  |
  +-----------------------------------------------------------------+
  |                 AddressList := {OrigAddr, TargAddr}             |
  +-----------------------------------------------------------------+
  | PrefixLengthList := {PrefixLength for OrigAddr, null}(optional) |
  +-----------------------------------------------------------------+
  |                 OrigSeqNum, (optional) TargSeqNum               |
  +-----------------------------------------------------------------+
  |                      MetricType (optional)                      |
  +-----------------------------------------------------------------+
  |             MetricList := {Metric for OrigAddr, null}           |
  +-----------------------------------------------------------------+
  | ValidityTimeList := {ValidityTime for OrigAddr, null}(optional) |
  +-----------------------------------------------------------------+

Figure 1: RREQ message structure

RREQ Data Elements
msg_hop_limit

The remaining number of hops allowed for dissemination of the RREQ message.
msg_hop_count

The number of hops already traversed during dissemination of the RREQ message.
AddressList

AddressList contains OrigAddr and TargAddr.
PrefixLengthList

PrefixLengthList contains the length of the prefix for OrigAddr, if OrigAddr resides on a Client Network with a prefix length shorter than the number of bits of the address family for OrigAddr.
OrigSeqNum

OrigSeqNum is REQUIRED and carries the destination sequence number associated with OrigNode.
TargSeqNum

TargSeqNum is optional and carries a destination sequence number associated with TargNode.
MetricList

The MetricList data element is REQUIRED, and carries the route metric information associated with OrigAddr.
MetricType

The MetricType element defines the type of Metric associated with the entries in the MetricList.
ValidityTimeList

The ValidityTimeList is optional and carries the length of time that the sender is willing to offer a route towards OrigAddr.

RREQ messages carry information about OrigAddr and TargAddr, as identified in the context of the RREQ_Gen. The OrigSeqNum MUST appear. Both MAY appear in the same RREQ when SeqNum is available for both OrigAddr and TargAddr.

The OrigSeqNum data element in a RteMsg MUST apply only to OrigAddr. The other address in the AddressList is TargAddr.

If the TargSeqNum data element appears, then it MUST apply only to TargAddr. The other address in the AddressList is OrigAddr.

9.1.1. RREQ Generation

Upon receiving an IP packet from one of its Router Clients, it often happens that an AODVv2 router has no valid route to the destination. In this case the AODVv2 router is responsible for generating a RREQ and associated data elements on behalf of its client OrigNode. The router is referred to as RREQ_Gen. Before creating a RREQ, RREQ_Gen should check if an RREQ has recently been sent for this destination and a response is awaited, or if the limit of AODVv2 RREQ retries has been reached.

In constructing the RREQ, RREQ_Gen uses AddressList, OrigSeqNum, MetricList, and optionally PrefixLengthList, TargSeqNum, MetricType, and ValidityTime.

RREQ_Gen follows the steps in this section. OrigAddr MUST be a unicast address. The order of data elements is illustrated schematically in Figure 1. RREQ_Gen SHOULD include TargSeqNum, if a previous value of the TargAddr's SeqNum is known (e.g. from an invalid route table entry using longest-prefix matching). If TargSeqNum is not included, AODVv2 routers handling the RREQ assume that RREQ_Gen does not have that information.

  1. Set msg_hop_limit to MAX_HOPCOUNT.
  2. Set msg_hop_count to zero, if including it.
  3. Set AddressList := {OrigAddr, TargAddr}.
  4. For the PrefixLengthList:
    • If OrigAddr resides on a subnet of Router Clients, set PrefixLengthList := { OrigAddr subnet's prefix, null }.
    • Otherwise, the PrefixLengthList is omitted.

  5. For the Sequence Number List:
    • Increment the SeqNum as specified in Section 6.4.
    • Set OrigSeqNum to the new value of SeqNum.
    • If an Invalid route exists matching TargAddr using longest prefix matching, include TargSeqNum and set it to the sequence number on the Invalid route. Otherwise omit TargSeqNum.

  6. Set MetricList := { Route[OrigAddr].Metric, null }.
  7. Include the MetricType data element if requesting a route for a non-default metric type.
  8. If the RREQ_Gen wishes to limit the time that the route to OrigAddr may be used, include the ValidityTime data element.

9.1.2. RREQ Reception

Upon receiving an RREQ, an AODVv2 router performs the following steps.

  1. A router MUST handle RREQs only from neighbors. RREQs from nodes that are not neighbors MUST be disregarded.
  2. Check whether the sender is on the blacklist of AODVv2 routers (see Section 6.2). If not, continue processing. Otherwise, check the Blacklist Remove Time.
    • If Current_Time < Remove Time, ignore this RREQ for further processing.
    • If Current_Time ≥ Remove Time, remove the Blacklist entry and continue processing.

  3. Verify that the message contains the required data elements: msg_hop_limit, OrigAddr, TargAddr, OrigSeqNum, OrigAddrMetric, and verify that OrigAddr and TargAddr are valid addresses (routable and unicast). If not, ignore this message for further processing.
  4. If the MetricType data element is present, check that the MetricType is known.
    • If not, ignore this RREQ for further processing.
    • Otherwise continue processing .

  5. Verify that OrigAddrMetric ≤ {MAX_METRIC[MetricType] - Cost(Link)}.
    • If not, ignore this RREQ for further processing.
    • Otherwise continue processing .

  6. Process the route to OrigAddr as specified in Section 8.1.
  7. Check if the message is a duplicate or redundant by comparing to entries in the RteMsg table as described in Section 8.6.
    • If duplicate or redundant, ignore this RREQ for further processing.
    • Otherwise save the information in the RteMsg table to identify future duplicates and continue processing.

  8. Check if the TargAddr belongs to one of the Router Clients.
    • If so, generate a RREP as specified in Section 9.2.1.
    • Otherwise, continue to RREQ regeneration.

9.1.3. RREQ Regeneration

Unless the router is prepared to advertise the new route, it halts processing. By sending a RREQ, a router advertises that it will forward packets to the OrigAddr contained in the RREQ according to the information enclosed. The router MAY choose not to regenerate the RREQ, though this could decrease connectivity in the network or result in non-optimal paths.

The circumstances under which a router MAY choose not to regenerate a RREQ are not specified in this document. Some examples may include the router being heavily loaded and not advertising routing for more traffic, or being low on energy and having to reduce energy expended for sending AODVv2 messages or packet forwarding.

The procedure for RREQ regeneration is as follows:

  1. Check the msg_hop_limit.
    • If it is zero, do not regenerate.
    • Otherwise, decrement the value by one.

  2. Check if msg_hop_count is present and greater than or equal to MAX_HOPCOUNT
    • If so, do not regenerate.
    • Otherwise, increment msg_hop_count by one.

  3. Change OrigAddrMetric to match the route table entry for OrigAddr, which should match the advertised value in the received RREQ plus the cost of the link to the router which forwarded the RREQ.
  4. If the incoming RREQ contains a ValidityTimeList, it MUST be copied into the regenerated RREQ. If not present, and the regenerating router wishes to limit the time that its route to OrigAddr may be used, set ValidityTimeList := {ValidityTime for OrigAddr, null}.

If the received RREQ was unicast, the regenerated RREQ can be unicast to the next hop address of the route towards TargAddr, if known. Otherwise, the RREQ SHOULD be multicast to the LL-MANET-Routers IP and MAC address [RFC5498], [RFC4291].

9.2. RREP Messages

RREP messages are used to offer a route to a target address, and are sent in response to a RREQ message. RREP messages have the following general structure:

  +-----------------------------------------------------------------+
  |                   msg_hop_limit, msg_hop_count                  |
  +-----------------------------------------------------------------+
  |                       AckReq (optional)                         |
  +-----------------------------------------------------------------+
  |                 AddressList := {OrigAddr,TargAddr}              |
  +-----------------------------------------------------------------+
  | PrefixLengthList := {null, PrefixLength for TargAddr(optional)} |
  +-----------------------------------------------------------------+
  |                            TargSeqNum                           |
  +-----------------------------------------------------------------+
  |            MetricList := {null, metric for TargAddr}            |
  +-----------------------------------------------------------------+
  |                     MetricType (optional)                       |
  +-----------------------------------------------------------------+
  | ValidityTimeList := {null, ValidityTime for TargAddr}(optional) |
  +-----------------------------------------------------------------+

Figure 2: RREP message structure

RREP Data Elements
msg_hop_limit

The remaining number of hops allowed for dissemination of the RREP message.
msg_hop_count

The number of hops already traversed during dissemination of the RREP message.
AckReq

Acknowledgement Requested by sender (optional).
AddressList

AddressList contains OrigAddr and TargAddr.
PrefixLengthList

PrefixLengthList contains the length of the prefix for TargAddr, if TargAddr resides on a Client Network with a prefix length shorter than the number of bits of the address family for TargAddr.
TargSeqNum

TargSeqNum is REQUIRED and carries the destination sequence number associated with TargNode.
MetricList

The MetricList data element is REQUIRED, and carries the route metric information associated with TargAddr.
MetricType

The MetricType element defines the type of Metric associated with the entries in the MetricList.
ValidityTimeList

The ValidityTimeList is optional and carries the length of time that the sender is willing to offer a route towards TargAddr.

RREP messages carry information about OrigAddr and TargAddr, as known in the context of the RREP_Gen. The TargSeqNum MUST appear. It MUST apply only to TargAddr. The other address in the AddressList is OrigAddr.

9.2.1. RREP Generation

This section specifies the generation of an RREP by an AODVv2 router (RREP_Gen) that provides connectivity for TargAddr, thus enabling the establishment of a route between OrigAddr and TargAddr. In constructing the RREP, AODVv2 uses AddressList, TargSeqNumber List, MetricList, and optionally AckReq, PrefixLengthList and/or ValidityTimeList. These elements are then used to create a RFC5444 message; see Section 10 for details.

The AckReq data element indicates that an acknowledgement to the RREP has been requested. If no corresponding RREP_Ack is received within the RREP_Ack_SENT_TIMEOUT, the next hop is added to the blacklist as discussed in Section 6.2.

The procedure for RREP generation is as follows:

  1. Set msg_hop_limit to the msg_hop_count from the received RREQ message.
  2. Set msg_hop_count, if including it, to zero.
  3. Include the AckReq data element if RREP_Ack is requested from the next hop (as described in Section 6.2).
  4. Include the MetricType data element and set the type accordingly.
  5. Set the Address List := {OrigAddr, TargAddr}.
  6. For the PrefixLengthList:
    • If TargAddr resides on a subnet of Router Clients, set PrefixLengthList := {null, TargAddr subnet's prefix}.
    • Otherwise, no PrefixLengthList is needed.

  7. For the TargSeqNum:
    • RREP_Gen increments its SeqNum as specified in Section 6.4.
    • Set TargSeqNum := the new value of SeqNum.

  8. Set MetricList := { null, Route[TargAddr].Metric }.
  9. If the RREP_Gen wishes to limit the time that the route to TargAddr may be used, set ValidityTimeList := {null, TargAddr ValidityTime}.

By default, the RREP is sent by unicast to the IP address of the next hop of the RREP_Gen's route to OrigAddr.

9.2.2. RREP Reception

Upon receiving an RREP, an AODVv2 router performs the following steps.

  1. Verify that the RREP message contains the required data elements: msg_hop_limit, OrigAddr, TargAddr, TargAddrMetric, TargSeqNum, and verify that OrigAddr and TargAddr are valid addresses (routable and unicast). If not, ignore this RREP message for further processing.
  2. Check that the MetricType is known.
    • If not, ignore this RREP for further processing.
    • Otherwise continue processing .

  3. Verify that TargAddrMetric ≤ {MAX_METRIC[MetricType] - Cost(Link)}.
    • If not, ignore this RREP for further processing.
    • Otherwise continue processing .

  4. Process the route to TargAddr as specified in Section 8.1.
  5. If the AckReq data element is present, send a RREP_Ack as specified in Section 9.4.
  6. Check if the message is a duplicate or redundant by comparing to entries in the RREP table as described in Section 8.6.
    • If duplicate or redundant, ignore this RREP for further processing.
    • Otherwise save the information in the RREP table to identify future duplicates and continue processing.

  7. Check if the OrigAddr belongs to one of the Router Clients.
    • If so, the RREP satisfies a previously sent RREQ. Processing is complete and data can now be forwarded along the route. Any packets from OrigAddr that were buffered for later delivery SHOULD be transmitted.
    • Otherwise, continue to RREP regeneration.

9.2.3. RREP Regeneration

Similar to rules for RREQ regeneration, unless the router is prepared to advertise the route to TargAddr, it halts processing. By forwarding a RREP, a router advertises that it will forward packets to the TargAddr contained in the RREP according to the information enclosed. The router MAY choose not to regenerate the RREP, for the same reasons as mentioned under RREQ regeneration Section 9.1.3, though this could decrease connectivity in the network or result in non-optimal paths.

If no valid route exists to OrigAddr, a RERR SHOULD be transmitted to TargAddr as specified in Section 9.3.1 and the RREP should not be regenerated.

The procedure for RREP regeneration is as follows:

  1. Check the msg_hop_limit.
    • If it is zero, do not regenerate.
    • Otherwise, decrement the value by one.

  2. If msg_hop_count is present, then:
    • If msg_hop_count ≥ MAX_HOPCOUNT, do not regenerate.
    • Otherwise, increment msg_hop_count by one.

  3. The RREP SHOULD be unicast to the next hop on the route to OrigAddr. If no valid route exists to OrigAddr, a RERR SHOULD be transmitted to TargAddr as specified in Section 9.3.1.
  4. Change TargAddrMetric to match the route table entry for TargAddr, which should match the advertised value in the received RREP plus the cost of the link to the router which forwarded the RREP.
  5. Include the AckReq data element if this device requires acknowledgement of the RREP message.
  6. If the incoming RREP contains a ValidityTimeList, it MUST be copied into the regenerated RREP. If not present, and the regenerating router wishes to limit the time that its route to TargAddr may be used, set ValidityTimeList := {null, ValidityTime for TargAddr}.

The RREP SHOULD be unicast to the next hop on the route to OrigAddr.

9.3. RERR Messages

  +-----------------------------------------------------------------+
  |                          msg_hop_limit                          |
  +-----------------------------------------------------------------+
  |                      PktSource (optional)                       |
  +-----------------------------------------------------------------+
  |                         RERR AddressList                        |
  +-----------------------------------------------------------------+
  |       PrefixLengthList for UnreachableAddresses (optional)      |
  +-----------------------------------------------------------------+
  |                SeqNumList (one entry per address)               |
  +-----------------------------------------------------------------+
  |                     MetricType (optional)                       |
  +-----------------------------------------------------------------+
        

Figure 3: RERR message structure

An RERR message is generated by a AODVv2 router (i.e., RERR_Gen) in order to notify upstream routers that packets cannot be delivered to one or more destinations. An RERR message has the following general structure:

RERR Data Elements
msg_hop_limit

The remaining number of hops allowed for dissemination of the RERR message.
PktSource

The IP address of the unreachable destination triggering RERR generation. If this RERR message was triggered by a broken link, the PktSource data element is not required.
RERR AddressList

A list of IP addresses not reachable by the AODVv2 router transmitting the RERR.
PrefixLengthList

PrefixLengthList contains the prefix lengths associated with the addresses in the RERR AddressList, if any of them reside on a Client Network with a prefix length shorter than the number of bits of their address family.
MetricType

If MetricType != DEFAULT_METRIC_TYPE, the MetricType associated with routes affected by a broken link.
SeqNumList

The list of sequence numbers associated with the UnreachableAddresses in the RERR AddressList.

9.3.1. RERR Generation

There are two types of events which trigger generation of a RERR message. The first is the arrival of a packet for which there is no route to the destination address. This can be a packet forwarded by the routing process, or a RREP when there is no route to OrigAddr. In this case, exactly one UnreachableAddress will be included in RERR's AddressList (either the Destination Address of the IP header from a data packet, or the OrigAddr found in the AddressList of an RREP message). RERR_Gen MUST discard the packet or message that triggered generation of the RERR.

The second type of event happens when a link breaks. All routes (whether valid or not) that use the broken link MUST be marked as Invalid. If the broken link was not used by any Active route, no RERR message is generated. Every Invalid route reported in the RERR MUST have the same MetricType. If the broken link affects routes to destinations that have different MetricTypes, multiple RERR messages must be generated.

If an AODVv2 router receives an ICMP packet to or from the address of one of its client nodes, it simply forwards the ICMP packet, and does not generate any RERR message.

In constructing the RERR, AODVv2 uses MetricType, AddressList, SeqNumList, and in some cases PktSource and PrefixLengthList. These elements are then used to create a RFC5444 message; see Section 10 for details.

The procedure for RERR generation is as follows:

  1. Set msg_hop_limit to MAX_HOPCOUNT.
  2. If the RERR was triggered by an Undeliverable Packet, the PktSource data element MUST be included, containing the source IP address of the Undeliverable Packet.
  3. Include the MetricType data element if reporting a Invalid route for a non-default metric type.
  4. For the RERR AddressList:
    • If the RERR was triggered by an undeliverable packet, insert the destination IP address of the undeliverable packet, or if the packet was a RREP, insert the OrigAddr.
    • If the RERR was triggered by a broken link, include the addresses of all previously Active routes which are now Invalid, up to the limit imposed by the MTU (interface "Maximum Transfer Unit") of the physical medium. If there are too many such previously Active routes, additional RERR messages should be constructed and transmitted to contain the remaining addresses. If the configuration option ENABLE_IDLE_IN_RERR is enabled, include any previously Idle routes which are now Invalid, as long as the packet size of the RERR does not exceed the MTU.

  5. If there are destinations reported in the RERR AddressList that have associated subnet prefixes in the route table, insert those prefixes in the PrefixLengthList; otherwise, omit the PrefixLengthList.
  6. If known, the sequence numbers associated with the routes to the addresses in the RERR AddressList SHOULD be included in the SeqNumList; otherwise, omit the SeqNumList.

If the RERR is sent in response to an Undeliverable Packet:

  • It SHOULD be sent unicast to the next hop towards the source IP address of the packet which triggered the RERR.
  • Otherwise the RERR MUST be sent to the multicast IP and MAC address for LL-MANET-Routers.

If the RERR is sent in response to a broken link:

  • If precursor lists are maintained for the addresses in the RERR AddressList (see Section 12.2), the RERR SHOULD be unicast to the precursors.
  • Otherwise the RERR MUST be sent to the multicast IP and MAC address for LL-MANET-Routers.

9.3.2. RERR Reception

Upon receiving an RERR, the following steps are performed.

  1. If the message does not contain the msg_hop_limit and at least one UnreachableAddress, do not process the RERR.
  2. If the MetricType data element is present, check that the MetricType is known.
    • If not, ignore this RERR for further processing.
    • Otherwise continue processing .

  3. For each UnreachableAddress,
    • Check that the address is valid (routable and unicast).
    • Check that there is a valid route with the same MetricType matching the address using longest prefix matching.
    • Check that the route's next hop is the sender of the RERR.
    • Check that the route's next hop interface is the interface on which the RERR was received.
    • Check that the Unreachable Address SeqNum is either unknown, or is greater than the route's SeqNum.
    • If any of the above are false, the UnreachableAddress does not need to be advertised in a regenerated RERR.
    • If all of the above are true:
      • If the route's prefix length is the same as the UnreachableAddress's prefix length, set the route state to Invalid.
      • If the prefix length is shorter than the original route, the route MUST be expunged from the routing table, since it is a sub-route of the larger route which is reported to be Invalid.
      • If the prefix length is different, create a new route with the UnreachableAddress and its prefix, and set the state to Invalid.

If there are no UnreachableAddresses which need to be advertised in a regenerated RERR, take no further action.

Otherwise regenerate the RERR as specified in Section 9.3.3.

9.3.3. RERR Regeneration

The procedure for RERR regeneration is as follows:

  1. Check the msg_hop_limit.
    • If it is zero, do not regenerate.
    • Otherwise, decrement the value by one.

  2. If the PktSource data element was included in the original RERR, copy it into the regenerated RERR.
  3. For the RERR AddressList, include all UnreachableAddresses which have been determined to need regeneration.
  4. For the PrefixLengthList, insert the prefix lengths associated with the addresses in the RERR AddressList.
  5. For the SeqNumList, include the sequence numbers corresponding to the addresses in the RERR AddressList.

If the original RERR contained the PktSource data element, and a route exists to the source address, the regenerated RERR MUST be sent unicast to the next hop of the route towards PktSource.

Otherwise, if precursor lists are maintained, the regenerated RERR SHOULD be sent to the active precursors of the Invalid routes as specified in Section 12.2.

Otherwise the regenerated RERR MUST be sent to the multicast IP and MAC address for LL-MANET-Routers.

9.4. RREP_Ack Messages

RREP_Ack is modeled on the RREP_Ack message type from AODV [RFC3561]. RREP_Ack messages have the following general structure:

  +-----------------------------------------------------------------+
  |                       msg_hop_limit := 1                        |
  +-----------------------------------------------------------------+

Figure 4: RREP_Ack message structure

RREP_Ack Data Elements
msg_hop_limit

The remaining number of hops allowed for dissemination of the RREP_Ack message.

9.4.1. RREP_Ack Generation

This section specifies the generation of an RREP_Ack by an AODVv2 router. The procedure is as follows:

  1. Set msg_hop_limit := 1.

The RREP_Ack is sent by unicast to the IP address of router that inserted a AckReq data element into a RREP message.

9.4.2. RREP_Ack Reception

Upon receiving an RREP_Ack, an AODVv2 router performs the following steps.

  1. The router checks whether the sender's IP address is in the blacklist. If so, the IP address is deleted from the blacklist.
  2. The router checks whether an RREP_Ack message was expected from the sending IP address, in response to an AckReq data element that the router included in a preceding RREP message as specified in Section 9.2.1. If so, the router records that the required RREP_Ack has been received and cancels the associated timeout.

10. Representing AODVv2 data elements using RFC 5444

AODVv2 specifies that all control plane messages between Routers SHOULD use the Generalised Mobile Ad-hoc Network Packet and Message Format [RFC5444], which provides a multiplexed transport for multiple protocols. AODVv2 therefore specifies Route Messages comprising data elements that map to message elements in RFC5444 but, in line with the concept of use, does not specify which order the messages should be arranged in an RFC5444 packet. An implementation of an RFC5444 multiplexer may choose to optimise the content of certain message elements to reduce control plane overhead. For handling of messages that contain unknown TLV types, the multiplexer SHOULD ignore the information for processing, but preserve it unmodified for forwarding.

Here is a brief summary of the RFC 5444 format.

  1. A packet formatted according to RFC 5444 contains zero or more messages.
  2. A message contains a message header, message TLV block, and zero or more address blocks.
  3. Each address block MAY also have one TLV blocks; each TLV block MAY encode any number of TLVs (including zero). Each TLV value in an Address TLV block is associated with exactly one of the addresses in the address block.

The following table shows how AODVv2 data elements are represented in RFC 5444 messages.

Data Element RFC 5444 Message Representation
msg_hop_limit RFC 5444 Message Header <msg-hop-limit>
msg_hop_count RFC 5444 Message Header <msg-hop-count>
AckReq Acknowledgement Request Message TLV
PktSource The Packet Source Message TLV
RteMsg AddressList RFC 5444 Address Block
-   OrigAddr
-   TargAddr
-   PrefixLengthList
RERR AddressList RFC 5444 Address Block
-   UnreachableAddress
-   PrefixLengthList
SeqNumList Sequence Number Address Block TLV
-   SeqNum
OrigSeqNum Originating Node Sequence Number Address Block TLV
TargSeqNum Target Node Sequence Number Address Block TLV
MetricType Extension byte of Metric Address Block TLV
MetricList Metric Address Block TLV
-   OrigAddrMetric - corresponds to OrigAddr
-   TargAddrMetric - corresponds to TargAddr
ValidityTimeList VALIDITY_TIME Address Block TLV
-   ValidityTime

AODVv2 neither requires any inclusion nor uses any information from the packet header. The length of an address (32 bits for IPv4 and 128 bits for IPv6) inside an AODVv2 message is indicated by the msg-addr-length (MAL) in the msg-header. Although the addresses in an Address Block may appear in any order, each TLV value in a TLV Block is associated with exactly one Address in the Address Block. So, for instance, the ordering of the OrigAddrMetric and TargAddrMetric values in the MetricList is determined by the order of OrigAddr and TargAddr in the preceding RteMsg Address List. See Section 14.2 for more information about AODVv2 Message TLVs. See Section 14.3 for more information about AODVv2 Address Block TLVs.

11. Simple Internet Attachment

Simple Internet attachment means attachment of a stub (i.e., non-transit) network of AODVv2 routers to the Internet via a single Internet AODVv2 router (called IAR).

As in any Internet-attached network, AODVv2 routers, and their clients, wishing to be reachable from hosts on the Internet MUST have IP addresses within the IAR's routable and topologically correct prefix (e.g. 191.0.2.0/24).

     /-------------------------\
    / +----------------+        \
   /  |  AODVv2 Router |         \
   |  |  191.0.2.2/32  |         |
   |  +----------------+         |            Routable
   |                       +-----+--------+   Prefix
   |                       |   Internet   |  /191.0.2/24
   |                       | AODVv2 Router| /
   |                       |  191.0.2.1   |/      /---------------\
   |                       | serving net  +------+    Internet     \
   |                       |  191.0.2/24  |      \                 /
   |                       +-----+--------+       \---------------/
   |         +----------------+  |
   |         |  AODVv2 Router |  |
   |         |  191.0.2.3/32  |  |
   \         +----------------+  /
    \                           /
     \-------------------------/

Figure 5: Simple Internet Attachment Example

When an AODVv2 router within the AODVv2 MANET wants to discover a route toward a node on the Internet, it uses the normal AODVv2 route discovery for that IP Destination Address. The IAR MUST respond to RREQ on behalf of all Internet destinations.

When a packet from a node on the Internet destined for a node in the AODVv2 MANET reaches the IAR, if the IAR does not have a route toward that destination it will perform normal AODVv2 route discovery for that destination.

12. Optional Features

Some optional features of AODVv2, associated with AODV, are not required by minimal implementations. These features are expected to apply in networks with greater mobility, or larger node populations, or requiring reduced latency for application launches. The optional features are as follows:

  • Expanding Rings Multicast
  • Precursor lists.
  • Multicast RREP Response to RREQ
  • Intermediate RREPs (iRREPs): Without iRREP, only the destination can respond to a RREQ.
  • Message Aggregation Delay.

12.1. Expanding Rings Multicast

For multicast RREQ, msg_hop_limit MAY be set in accordance with an expanding ring search as described in [RFC3561] to limit the RREQ propagation to a subset of the local network and possibly reduce route discovery overhead.

12.2. Precursor Lists and Notifications

This section specifies an interoperable enhancement to AODVv2 (and possibly other reactive routing protocols) enabling more economical RERR notifications to traffic sources upon determination that a route needed to forward such traffic to its destination has become Invalid.

12.2.1. Overview

In many circumstances, there can be several sources of traffic for a certain destination. Each such source of traffic is known as a "precursor" for the destination, as well as all upstream routers between the forwarding AODVv2 router and the traffic source. There is no need to keep track of upstream routers any farther away than the next hop. For each destination, an AODVv2 router MAY choose to keep track of the upstream neighbors that have provided traffic for that destination.

Moreover, any particular link to an adjacent AODVv2 router may be a path component of multiple routes towards various destinations. The precursors for all destinations using the next hop across any link are collectively known as the precursors for that next hop.

When an AODVv2 router marks a route as Invalid, the precursors of the Invalid route should be notified (using RERR) about the change in status of their route to the destination of that Invalid route.

12.2.2. Precursor Notification Details

During normal operation, each AODVv2 router wishing to maintain precursor lists as described above, maintains a precursor table and updates the table whenever the node forwards traffic to one of the destinations in its route table. For each precursor in the precursor list, a record must be maintained to indicate whether the precursor has been used for recent traffic (in other words, whether the precursor is an Active precursor). So, when traffic arrives from a precursor, the Current_Time is used to mark the time of last use for the precursor list element associated with that precursor.

When an AODVv2 router detects that a link is broken, then for each Active precursor using that next hop, the node MAY notify the precursor using either unicast or multicast RERR:

unicast RERR to each Active precursor

This option is applicable when there are few Active precursors compared to the number of neighboring AODVv2 routers.
multicast RERR to RERR_PRECURSORS

RERR_PRECURSORS is, by default, LL-MANET-Routers [RFC5498]. This option is typically preferable when there are many precursors, since fewer packet transmissions are required.

Each neighbor receiving the RERR MAY then execute the same procedure until all upstream routers have received the RERR notification.

12.3. Multicast RREP Response to RREQ

The RREQ Target Router (RREP_Gen) MAY, as an alternative to unicasting a RREP, be configured to use multicast to distribute routing information about the route toward TargAddr. RREP_Gen does this as described in Section 9.2.1, but multicasting the RREP to LL-MANET-Routers [RFC5498]. Routers receiving the multicast RREP must perform RteMsg suppression (see Section 8.6).

Broadcast RREP response to incoming RREQ was originally specified to handle unidirectional links, but it is expensive. Due to the significant overhead, AODVv2 routers MUST NOT use multicast RREP unless configured to do so by setting the administrative parameter USE_MULTICAST_RREP. This technique can be used to find the best return path rather than follow the same path as the RREQ took.

12.4. Intermediate RREP

This specification has been published as a separate Internet Draft [I-D.perkins-irrep].

12.5. Message Aggregation Delay

The aggregation of multiple messages into a packet is specified in RFC 5444 [RFC5444].

Implementations MAY choose to briefly delay transmission of messages for the purpose of aggregation (into a single packet) or to improve performance by using jitter [RFC5148].

13. Administratively Configurable Parameters and Timer Values

AODVv2 uses various configurable parameters of various types:

  • Timers
  • Protocol constants
  • Administrative (functional) controls
  • Other administrative parameters and lists

The tables in the following sections show the parameters along their definitions and default values (if any).

Note: several fields have limited size (bits or bytes). These sizes and their encoding may place specific limitations on the values that can be set. For example, <msg-hop-count> is a 8-bit field and therefore MAX_HOPCOUNT cannot be larger than 255.

13.1. Timers

AODVv2 requires certain timing information to be associated with route table entries. The default values are as follows:

Timing Parameter Values
Name Default Value
ACTIVE_INTERVAL 5 second
MAX_IDLETIME 200 seconds
MAX_BLACKLIST_TIME 200 seconds
MAX_SEQNUM_LIFETIME 300 seconds
RteMsg_ENTRY_TIME 12 seconds
RREQ_WAIT_TIME 2 seconds
RREP_Ack_SENT_TIMEOUT 1 second
RREQ_HOLDDOWN_TIME 10 seconds

The above timing parameter values have worked well for small and medium well-connected networks with moderate topology changes. The timing parameters SHOULD be administratively configurable for the network where AODVv2 is used. Ideally, for networks with frequent topology changes the AODVv2 parameters should be adjusted using either experimentally determined values or dynamic adaptation. For example, in networks with infrequent topology changes MAX_IDLETIME may be set to a much larger value.

13.2. Protocol Constants

AODVv2 protocol constants typically do not require changes. The following table lists these constants, along with their values and a reference to the specification describing their use.

Parameter Values
Name Default Value Description
DISCOVERY_ATTEMPTS_MAX 3 Section 8.5
MAX_HOPCOUNT 20 hops Section 7
MAX_METRIC[i] Specified only for HopCount Section 7
MAXTIME [TBD] Maximum expressible clock time Section 8.4

These values MUST have the same values for all AODVv2 routers in the ad hoc network. If the configured values are different, the following consequences may be observed:

  • DISCOVERY_ATTEMPTS_MAX: some nodes are likely to be more successful at finding routes, but at the cost of additional control traffic for unsuccessful attempts.
  • MAX_HOPCOUNT: If some nodes use a value that is too small, they would not be able to discover routes to distant addresses.
  • MAX_METRIC[DEFAULT_METRIC_TYPE]: MUST always be the maximum expressible metric of type DEFAULT_METRIC_TYPE. No interoperability problems due to variations on different nodes, but if a lesser value is used, route comparisons may exhibit overly restrictive behavior.
  • MAXTIME: Variations on different nodes would not cause problems for interoperability. If a lesser value is used, route state management may exhibit overly restrictive behavior.

13.3. Administrative (functional) controls

The following administrative controls may be used to change the operation of the network, by enabling optional behaviors. These options are not required for correct routing behavior, although they may potentially reduce AODVv2 protocol messaging in certain situations. The default behavior is typically to NOT enable the options. Inconsistent settings at different nodes in the network will not result in protocol errors. In the case of inconsistent settings for DEFAULT_METRIC_TYPE, inconsistent setting might result in messages specifying metric types unknown to some nodes and consequent poor performance.

Administratively Configured Controls
Name Description
DEFAULT_METRIC_TYPE 3 (i.e, Hop Count (see [RFC6551]))
ENABLE_IDLE_IN_RERR Section 9.3.1
ENABLE_IRREP Section 9.1.1
USE_MULTICAST_RREP Section 12.3

13.4. Other administrative parameters and lists

The following table lists contains AODVv2 parameters which should be administratively configured for each node.

Other Administrative Parameters
Name Default Value Cross Reference
AODVv2_INTERFACES Section 4
BUFFER_SIZE_PACKETS 2 Section 8.5
BUFFER_SIZE_BYTES MAX_PACKET_SIZE [TBD] Section 8.5
CLIENT_ADDRESSES AODVv2_INTERFACES Section 6.3
CONTROL_TRAFFIC_LIMIT TBD [50 packets/sec?] Section 9

14. IANA Considerations

This section specifies several RFC 5444 message types, message tlv-types, and address tlv-types. Also, a new registry of 16-bit alternate metric types is specified.

14.1. AODVv2 Message Types Specification

AODVv2 Message Types
Name of AODVv2 Message Type
Route Request (RREQ) 10 (TBD)
Route Reply (RREP) 11 (TBD)
Route Error (RERR) 12 (TBD)
Route Reply Acknowledgement (RREP_Ack) 13 (TBD)

14.2. Message TLV Type Specification

Message TLV Types
Name of Message TLV Type Length (octets) Cross Reference
AckReq (Acknowledgment Request) 10 (TBD) 0 Section 6.2
PktSource (Packet Source) 11 (TBD) 4 or 16 Section 9.3.1

14.3. Address Block TLV Specification

Address Block TLV (AddrTLV) Types
Name of Address Block TLV Type Length Value
Metric 10 (TBD) depends on MetricType Section 9.1
Sequence Number (SeqNum) 11 (TBD) 2 octets Section 9.1
Originating Node Sequence Number (OrigSeqNum) 12 (TBD) 2 octets Section 9.1
Target Node Sequence Number (TargSeqNum) 13 (TBD) 2 octets Section 9.1
VALIDITY_TIME 1 1 octet [RFC5497]

14.4. MetricType Number Allocation

Metric types are identified according to the assignments as specified in [RFC6551]. The metric type of the Hop Count metric is assigned to be 3, in order to maintain compatibility with that existing table of values from RFC 6551.

Metric Types
Name of MetricType Type Metric Size
Unallocated 0 -- 2 TBD
Hop Count 3 - TBD 1 octet
Unallocated 4 -- 254 TBD
Reserved 255 Undefined

15. Security Considerations

The objective of the AODVv2 protocol is for each router to communicate reachability information about addresses for which it is responsible. Positive routing information (i.e. a route exists) is distributed via RREQ and RREP messages. Negative routing information (i.e. a route does not exist) is distributed via RERRs. AODVv2 routers store the information contained in these messages in order to properly forward data packets, and they generally provide this information to other AODVv2 routers.

This section describes various security considerations and potential avenues to secure AODVv2 routing. Security for authentication of AODVv2 routers, and/or encryption of traffic is dealt with by the underlying transport mechanism (e.g., by using the techniques for Authentication, Integrity, and Confidentiality documented in [RFC5444]). The most important security mechanism for AODVv2 routing is integrity/authentication.

In situations where routing information are suspect, integrity and authentication techniques SHOULD be applied to AODVv2 messages. In these situations, routing information that is distributed over multiple hops SHOULD also verify the integrity of information based on originator of the routing information.

In situations where confidentiality of AODVv2 messages is important, cryptographic techniques can be applied.

In certain situations, for example sending a RREP or RERR, an AODVv2 router could include proof that it has previously received valid routing information to reach the destination, at one point of time in the past. In situations where routers are suspected of transmitting maliciously erroneous information, the original routing information along with its security credentials SHOULD be included.

Note that if multicast is used, any confidentiality and integrity algorithms used MUST permit multiple receivers to handle the message [RFC7182].

Routing protocols, however, are prime targets for impersonation attacks. In networks where the node membership is not known, it is difficult to determine the occurrence of impersonation attacks, and security prevention techniques are difficult at best. However, when the network membership is known and there is a danger of such attacks, AODVv2 messages must be protected by the use of authentication techniques, such as those involving generation of unforgeable and cryptographically strong message digests or digital signatures.

Most AODVv2 messages are transmitted to the multicast address LL-MANET-Routers [RFC5498]. It is therefore required for security that AODVv2 neighbors exchange security information that can be used to insert an ICV [RFC7182] into the AODVv2 message block [RFC5444]. This enables hop-by-hop security. For destination-only RREP discovery procedures, AODVv2 routers that share a security association SHOULD use the appropriate mechanisms as specified in [RFC7182]. The establishment of these security associations is out of scope for this document.

16. Acknowledgments

AODVv2 is a descendant of the design of previous MANET on-demand protocols, especially AODV [RFC3561] and DSR [RFC4728]. Changes to previous MANET on-demand protocols stem from research and implementation experiences. Thanks to Elizabeth Belding and Ian Chakeres for their long time authorship of AODV. Additional thanks to Derek Atkins, Emmanuel Baccelli, Abdussalam Baryun, Ramon Caceres, Thomas Clausen, Christopher Dearlove, Ulrich Herberg, Henner Jakob, Luke Klein-Berndt, Lars Kristensen, Tronje Krop, Koojana Kuladinithi, Kedar Namjoshi, Alexandru Petrescu, Henning Rogge, Fransisco Ros, Pedro Ruiz, Christoph Sommer, Lotte Steenbrink, Romain Thouvenin, Richard Trefler, Jiazi Yi, Seung Yi, and Cong Yuan, for their reviews AODVv2 and DYMO, as well as numerous specification suggestions.

17. References

17.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P. and C. Pignataro, "The Generalized TTL Security Mechanism (GTSM)", RFC 5082, October 2007.
[RFC5444] Clausen, T., Dearlove, C., Dean, J. and C. Adjih, "Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format", RFC 5444, February 2009.
[RFC5497] Clausen, T. and C. Dearlove, "Representing Multi-Value Time in Mobile Ad Hoc Networks (MANETs)", RFC 5497, March 2009.
[RFC5498] Chakeres, I., "IANA Allocations for Mobile Ad Hoc Network (MANET) Protocols", RFC 5498, March 2009.
[RFC6551] Vasseur, JP., Kim, M., Pister, K., Dejean, N. and D. Barthel, "Routing Metrics Used for Path Calculation in Low-Power and Lossy Networks", RFC 6551, March 2012.

17.2. Informative References

[I-D.perkins-irrep] Perkins, C. and I. Chakeres, "Intermediate RREP for dynamic MANET On-demand (AODVv2) Routing", Internet-Draft draft-perkins-irrep-02, November 2012.
[Perkins94] Perkins, C. and P. Bhagwat, "Highly Dynamic Destination-Sequenced Distance-Vector Routing (DSDV) for Mobile Computers", Proceedings of the ACM SIGCOMM '94 Conference on Communications Architectures, Protocols and Applications, London, UK, pp. 234-244, August 1994.
[Perkins99] Perkins, C. and E. Royer, "Ad hoc On-Demand Distance Vector (AODV) Routing", Proceedings of the 2nd IEEE Workshop on Mobile Computing Systems and Applications, New Orleans, LA, pp. 90-100, February 1999.
[RFC2501] Corson, M. and J. Macker, "Mobile Ad hoc Networking (MANET): Routing Protocol Performance Issues and Evaluation Considerations", RFC 2501, January 1999.
[RFC3561] Perkins, C., Belding-Royer, E. and S. Das, "Ad hoc On-Demand Distance Vector (AODV) Routing", RFC 3561, July 2003.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast Addresses", RFC 4193, October 2005.
[RFC4728] Johnson, D., Hu, Y. and D. Maltz, "The Dynamic Source Routing Protocol (DSR) for Mobile Ad Hoc Networks for IPv4", RFC 4728, February 2007.
[RFC4861] Narten, T., Nordmark, E., Simpson, W. and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007.
[RFC5148] Clausen, T., Dearlove, C. and B. Adamson, "Jitter Considerations in Mobile Ad Hoc Networks (MANETs)", RFC 5148, February 2008.
[RFC6130] Clausen, T., Dearlove, C. and J. Dean, "Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)", RFC 6130, April 2011.
[RFC6621] Macker, J., "Simplified Multicast Forwarding", RFC 6621, May 2012.
[RFC7182] Herberg, U., Clausen, T. and C. Dearlove, "Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)", RFC 7182, April 2014.

Appendix A. Example Algorithms for AODVv2 Protocol Operations

The following subsections show example algorithms for protocol operations required by AODVv2, including RREQ, RREP, RERR, and RREP_Ack.

Processing for RREQ, RREP, and RERR messages follows the following general outline:

  1. Receive incoming message.
  2. Update route table as appropriate.
  3. Respond as needed, often regenerating the incoming message with updated information.

Once the route table has been updated, the information contained there is known to be the most recent available information for any fields in the outgoing message. For this reason, the algorithms are written as if outgoing message field values are assigned from the route table information, even though it is often equally appropriate to use fields from the incoming message.

AODVv2_algorithms:

  • Process_Routing_Info
  • Fetch_Route_Table_Entry
  • Update_Route_Table_Entry
  • Create_Route_Table_Entry
  • LoopFree
  • Update_Rte_Msg_Table
  • Generate_RREQ
  • Receive_RREQ
  • Regenerate_RREQ
  • Generate_RREP
  • Receive_RREP
  • Regenerate_RREP
  • Generate_RERR
  • Receive_RERR
  • Regenerate_RERR
  • Generate_RREP_Ack
  • Receive_RREP_Ack
  • Timeout RREP_Ack

The following lists indicate the meaning of the field names used in subsequent sections to describe message processing for the above algorithms.

RteMsg parameters, where rteMsg can be inRREQ, outRREQ, inRREP or outRREP:

  • rteMsg.hopLimit
  • rteMsg.hopCount
  • rteMsg.ackReq (RREP only, optional)
  • rteMsg.metricType (optional)
  • rteMsg.origAddr
  • rteMsg.targAddr
  • rteMsg.origPrefixLen (optional)
  • rteMsg.targPrefixLen (optional)
  • rteMsg.origSeqNum (RREQ only)
  • rteMsg.targSeqNum (optional in RREQ)
  • rteMsg.origAddrMetric (RREQ only)
  • rteMsg.targAddrMetric (RREP only)
  • rteMsg.validityTime
  • rteMsg.nbrIP

AdvRte has the following properties as described in Section 8.1:

  • AdvRte.Address = OrigAddr (in a RREQ) or TargAddr (in a RREP)
  • AdvRte.PrefixLength = PrefixLength for OrigAddr (in a RREQ) or TargAddr (in a RREP), or if not present, the maximum address length for the address family of AdvRte.Address
  • AdvRte.SeqNum = SeqNum for OrigAddr (in a RREQ) or for TargAddr (in a RREP)
  • AdvRte.MetricType = RteMsg.MetricType
  • AdvRte.Metric = RteMsg.Metric
  • AdvRte.Cost = AdvRte.Metric + Cost(L) according to the indicated MetricType, where L is the link from the advertising router
  • AdvRte.ValidityTime = ValidityTime in the RteMsg, if present
  • AdvRte.NextHopIP = IP source of the RteMsg
  • AdvRte.NextHopIntf = interface the RteMsg was received on
  • AdvRte.HopCount = value from RteMsg header
  • AdvRte.HopLimit = value from RteMsg header
  • AdvRte.AckReq = true/false whether present in RteMsg (optional in RREP)

A route table entry has properties as described in Section 6.1:



























  • Route.Address
  • Route.PrefixLength
  • Route.SeqNum
  • Route.NextHop
  • Route.NextHopInterface
  • Route.LastUsed
  • Route.LastSeqNum
  • Route.ExpirationTime
  • Route.MetricType
  • Route.Metric
  • Route.State
  • Route.Timed
  • Route.Precursors (optional)

A.1. Subroutines for AODVv2 Operations

A.1.1. Process_Routing_Info

  /* Compare incoming route information to stored route, maybe use
     linkMetric: either Cost(inRREQ.netif) or (inRREP.netif) */
  Process_Routing_Info (advRte)
  {
    rte := Fetch_Route_Table_Entry (advRte);
    if (!rte exists)
    {
      rte := Create_Route_Table_Entry(advRte);
      return rte;
    }

    /* rule from 8.1 */
    if (
         (AdvRte.SeqNum > Route.SeqNum)  /* stored route is stale */
           OR
          ((AdvRte.SeqNum == Route.SeqNum)  /* same SeqNum */
            AND
          [( (Route.State == Invalid)
              AND
             (LoopFree(advRte, rte)))  /* advRte can repair stored */
            OR
       (AdvRte.Cost < Route.Metric)])) /* advRte is better */
    {
      Update_Route_Table_Entry (rte, advRte);
    }
    return rte;
  }





























A.1.2. Fetch_Route_Table_Entry

    /* lookup a route table entry matching an advertised route */
    Fetch_Route_Table_Entry (advRte)
    {
      foreach (rteTableEntry in rteTable)
      {
         if (rteTableEntry.Address == advRte.Address AND
             rteTableEntry.MetricType == advRte.MetricType)
         return rteTableEntry;
      }
      return null;
    }

    /* lookup a route table entry matching address and metric type */
    Fetch_Route_Table_Entry (destination, metricType)
    {
      foreach (rteTableEntry in rteTable)
      {
         if (rteTableEntry.Address == destination AND
             rteTableEntry.MetricType == metricType)
         return rteTableEntry;
      }
      return null;
    }





























A.1.3. Update_Route_Table_Entry

    /* update a route table entry using AdvRte in received RteMsg */
    Update_Route_Table_Entry (rte, advRte);
    {
      rte.SeqNum := advRte.SeqNum;
      rte.NextHop := advRte.NextHopIp;
      rte.NextHopInterface := advRte.NextHopIntf;
      rte.LastUsed := Current_Time;
      rte.LastSeqNum := Current_Time;
      if (validityTime)
      {
         rte.ExpirationTime := Current_Time + advRte.validityTime;
         rte.Timed := true;
      }
      else
      {
         rte.Timed := false;
         rte.ExpirationTime := MAXTIME;
      }

      rte.Metric := advRte.Cost;
      if (rte.State == Invalid)
        rte.State := Idle;
    }

A.1.4. Create_Route_Table_Entry

  /* Create a route table entry from address and prefix length */
  Create_Route_Table_Entry (address, prefixLength,
                                              seqNum, metricType)
  {
    rte := allocate_memory();
    rte.Address := address;
    rte.PrefixLength := prefixLength;
    rte.SeqNum := seqNum;
    rte.MetricType := metricType;
  }
  /* Create a route table entry from the advertised route */
  Create_Route_Table_Entry(advRte)
  {
    rte := allocate_memory();

    rte.Address := advRte.Address;
    if (advRte.PrefixLength)
      rte.PrefixLength := advRte.PrefixLength;
    else
      rte.PrefixLength := maxPrefixLenForAddressFamily;

    rte.SeqNum := advRte.SeqNum;
    rte.NextHop := advRte.NextHopIp;
    rte.NextHopInterface := advRte.NextHopIntf;
    rte.LastUsed := Current_Time
    rte.LastSeqnum := Current_Time
    if (validityTime)
    {
      rte.ExpirationTime := Current_Time + advRte.ValidityTime;
      rte.Timed := true;
    }
    else
    {
      rte.Timed := false;
      rte.ExpirationTime := MAXTIME;
    }
    rte.MetricType := advRte.MetricType;
    rte.Metric := advRte.Metric;
    rte.State := Idle;
  }

A.1.5. LoopFree

    /* return TRUE if the route advRte is LoopFree compared to rte */
    LoopFree(advRte, rte)
    {
      if (advRte.Cost ≤ rte.Cost)
         return true;
      else
         return false;
    }





























A.1.6. Fetch_Rte_Msg_Table_Entry

    /* Find an entry in the RteMsg table matching the given
       message's msg-type, OrigAddr, TargAddr, MetricType   */
    Fetch_Rte_Msg_Table_Entry (rteMsg)
    {
      foreach (entry in RteMsgTable)
      {
        if (entry.msg-type == rteMsg.msg-type AND
            entry.OrigAddr == rteMsg.OrigAddr AND
            entry.TargAddr == rteMsg.TargAddr AND
            entry.MetricType == rteMsg.MetricType)
        {
          return entry;
        }
      }
      return NULL;
    }

A.1.7. Update_Rte_Msg_Table

    /* update the multicast route message suppression table based
       on the received RteMsg, return true if it was created or
       the SeqNum was updated (i.e. it needs to be regenerated) */
    Update_Rte_Msg_Table(rteMsg)
    {
      /* search for a comparable entry */
      entry := Fetch_Rte_Msg_Table_Entry(rteMsg)

      /* if there is none, create one (see 6.5 and 8.6) */
      if (entry does not exist)
      {
        entry.MessageType := rteMsg.msg_type
        entry.OrigAddr := rteMsg.OrigAddr
        entry.TargAddr := rteMsg.TargAddr
        entry.OrigSeqNum := rteMsg.origSeqNum (if present)
        entry.TargSeqNum := rteMsg.targSeqNum (if present)
        entry.MetricType := rteMsg.MetricType 
        entry.Metric := rteMsg.origAddrMetric(for RREQ)
                     or rteMsg.targAddrMetric(for RREP) 
        entry.Timestamp := Current_Time
        return true;
      }
      /* if current entry is stale */
      if ( (rteMsg.msg-type == RREQ AND
                        entry.OrigSeqNum < rteMsg.OrigSeqNum)
           OR
           (rteMsg.msg-type == RREP AND
                        entry.TargSeqNum < rteMsg.TargSeqNum))
      {
        entry.OrigSeqNum := rteMsg.OrigSeqNum (if present)
        entry.TargSeqNum := rteMsg.TargSeqNum (if present)
        entry.Timestamp := Current_Time
        return true;
      }

      /* if received rteMsg is stale */
      if ( (rteMsg.msg-type == RREQ AND
                        entry.OrigSeqNum > rteMsg.OrigSeqNum)
           OR
           (rteMsg.msg-type == RREP AND
                        entry.TargSeqNum > rteMsg.TargSeqNum))
      {
        entry.Timestamp := Current_Time
        return false;
      }

      /* if same SeqNum but rteMsg has lower metric */
      if (entry.Metric > rteMsg.Metric)
        entry.Metric := rteMsg.Metric

      entry.Timestamp := Current_Time
      return false;
    }





























A.1.8. Build_RFC_5444_message_header

   /* This pseudocode shows possible RFC 5444 actions, and
      would not be performed by the AODVv2 implementation.
      It is shown only to provide more understanding about
      the AODVv2 message that will be constructed by RFC 5444 */
   Build_RFC_5444_message_header (msgType, Flags,
                 AddrFamily, Size, hopLimit, hopCount, tlvLength)
   {
      /* Build RFC 5444 message header fields */
      msg-type := msgType
      MF (Message Flags) := Flags
      MAL (Message Address Length) := 3 for IPv4, 15 for IPv6
      msg-size := Size (octets - counting MsgHdr, AddrBlk, AddrTLVs)
      msg-hop-limit := hopLimit
      if (hopCount != 0)    /* hopCount == 0 means do not include */
        msg-hop-count := hopCount
      msg.tlvs-length := tlvLength
   }

A.2. Example Algorithms for AODVv2 RREQ Operations

A.2.1. Generate_RREQ

    Generate_RREQ
    {
      /* Increment sequence number */
      mySeqNum := (1 + mySeqNum) /* from nonvolatile storage */

      /* Marshall parameters */
      outRREQ.hopLimit := MAX_HOPCOUNT   /* RFC 5444 */
      outRREQ.hopCount := (if included) 0
      outRREQ.metricType := if not DEFAULT_METRIC_TYPE,
                              metric type needed by application
      outRREQ.origAddr := IP address of Router Client which generated
                              the packet to be forwarded
      outRREQ.targAddr := destination IP address in
                              the packet to be forwarded
      outRREQ.origPrefixLen := if included, the prefix length
                              associated with the Router Client
      outRREQ.origSeqNum := mySeqNum
      outRREQ.targSeqNum := if known from route table,
                              target sequence number
      outRREQ.origAddrMetric := 0 (default) or
                                    MIN_METRIC(outRREQ.metricType)
      outRREQ.validityTime := if included, the validity time
                              for route to OrigAddr

      /* Build Address Blk */
      AddrBlk := outRREQ.origAddr and outRREQ.targAddr addresses
            /* using prefix length information from
               outRREQ.origPrefixLen if necessary */

      /* Include each available Sequence Number in appropriate
         Address Block TLV */
      /* OrigSeqNum Address Block TLV */
      origSeqNumAddrBlkTlv.value := outRREQ.origSeqNum

      /* TargSeqNum Address Block TLV */
      if (outRREQ.targSeqNum is known)
      {
        targSeqNumAddrBlkTlv.value := outRREQ.targSeqNum
      }

      /* Build Metric Address Block TLV */
      metricAddrBlkTlv.value := outRREQ.origAddrMetric
      if (outRREQ.metricType != DEFAULT_METRIC_TYPE)
      { /* include Metric AddrBlkTlv Extension byte */
        metricAddrBlkTlv.typeExtension := outRREQ.MetricType
      }

      if (outRREQ.validityTime is required)
      {
        /* Build VALIDITY_TIME Address Block TLV */
        VALIDITY_TIMEAddrBlkTlv.value := outRREQ.validityTime
      }

      /* multicast RFC 5444 message to LL-MANET-Routers */
    }

A.2.2. Receive_RREQ

   Receive_RREQ (inRREQ)
   {
     if (inRREQ.nbrIP present in blacklist) {
          if (blacklist_expiration_time < current_time)
             return;   /* don't process or regenerate RREQ... */
          else
            remove nbrIP from blacklist;
        }
     if (inRREQ does not contain msg_hop_limit, OrigAddr,
                             TargAddr, OrigSeqNum, OrigAddrMetric)
          return;

     if (inRREQ.origAddr and inRREQ.targAddr are not valid
                             routable and unicast addresses)
          return;

     if (inRREQ.metricType is present but an unknown value)
          return;

     if (inRREQ.origAddrMetric >
                       MAX_METRIC[inRREQ.metricType] - Cost(Link)
          return;

     /* Extract inRREQ values */
     advRte.Address = inRREQ.origAddr
     advRte.PrefixLength = inRREQ.origPrefixLen (if present),
                             or the maximum address length for the
                             address family of advRte.Address
     advRte.SeqNum = inRREQ.origSeqNum
     advRte.MetricType = inRREQ.metricType
     advRte.Metric = inRREQ.origAddrMetric
     advRte.Cost = inRREQ.origAddrMetric + Cost(L)
                    according to the indicated MetricType, where
                    L is the link from the advertising router
     advRte.ValidityTime = inRREQ.validityTime (if present)
     advRte.NextHopIP = inRREQ.nbrIP
     advRte.NextHopIntf = interface the RteMsg was received on
     advRte.HopCount = inRREQ.hopCount
     advRte.HopLimit = inRREQ.hopLimit

     rte = Process_Routing_Info (advRte)

     /* update the RteMsgTableand determine if the RREQ needs
        to be regenerated */
     regenerate = Update_Rte_Msg_Table(inRREQ)

     if (inRREQ.targAddr is in Router Client list)
        Generate_RREP(inRREQ, rte)
     else if (regenerate)
        Regenerate_RREQ(inRREQ, rte)
    }

A.2.3. Regenerate_RREQ

    Regenerate_RREQ (inRREQ, rte) /* called from receive_RREQ(),
                                rte is the route to OrigAddr */
    {
      outRREQ.hopLimit := inRREQ.hopLimit - 1
      if (outRREQ.hopLimit == 0)
        return; /* don't regenerate */

      if (inRREQ.hopCount exists)
      {
        if (inRREQ.hopCount >= MAX_HOPCOUNT)
          return; /* don't regenerate */
        outRREQ.hopCount := inRREQ.hopCount + 1
      }

      /* Marshall parameters */
      outRREQ.metricType := rte.MetricType
      outRREQ.origAddr := rte.Address
      outRREQ.targAddr := inRREQ.targAddr
      outRREQ.origPrefixLen := rte.PrefixLength
                              (if not equal to address length)
      outRREQ.origSeqNum := rte.SeqNum
      outRREQ.targSeqNum := inRREQ.targSeqNum /* if present */
      outRREQ.origAddrMetric := rte.Metric
      outRREQ.validityTime := rte.ValidityTime or length of time
                 HandlingRtr wishes to advertise route to OrigAddr


      /* Build Address Block */
      AddrBlk := outRREQ.origAddr and outRREQ.targAddr addresses
           using prefix length information from outRREQ.origPrefixLen
           if necessary

      /* Include available Sequence Numbers in Address Block TLV */
      /* OrigSeqNum Address Block TLV */
      origSeqNumAddrBlkTlv.value := outRREQ.origSeqNum

      /* TargSeqNum Address Block TLV */
      if (outRREQ.targSeqNum is known) {
        targSeqNumAddrBlkTlv.value := outRREQ.targSeqNum
      }

      /* Build Metric Address Block TLV */
      metricAddrBlkTlv.value = outRREQ.origAddrMetric
      if (outRREQ.metricType != DEFAULT_METRIC_TYPE)
      { /* include Metric AddrBlkTlv extension byte */
        metricAddrBlkTlv.typeExtension := outRREQ.MetricType
      }

      if (outRREQ.validityTime is required)
      {
        /* Build VALIDITY_TIME Address Block TLV */
        VALIDITY_TIMEAddrBlkTlv.value = outRREQ.validityTime
      }
      Build_RFC_5444_message_header (RREQ, 4, IPv4 or IPv6, NN,
                outRREQ.hopLimit, outRREQ.hopCount, tlvLength)

      /* multicast RFC 5444 message to LL-MANET-Routers, or if
         inRREQ was unicast the message can be unicast to the next
         hop on the route to TargAddr, if known */
    }

A.3. Example Algorithms for AODVv2 RREP Operations

A.3.1. Generate_RREP

    Generate_RREP(inRREQ, rte)
    {
      /* Increment Sequence Number */
      mySeqNum := (1 + mySeqNum) /* from nonvolatile storage */

      /* Marshall parameters */
      outRREP.hopLimit := inRREQ.hopCount
      outRREP.hopCount := 0
      /* Include the AckReq when:
         - previous RREP does not seem to enable any data flow, OR
         - when RREQ is received from same OrigAddr after RREP was
           unicast to rte.nextHop
      */
      outRREP.ackReq := if included, TRUE otherwise FALSE

      if (rte.metricType != DEFAULT_METRIC_TYPE)
           outRREP.metricType := rte.metricType
      outRREP.origAddr := rte.Address
      outRREP.targAddr := inRREQ.targAddr
      outRREP.targPrefixLen := rte.PrefixLength
                             (if not equal to address length)
      outRREP.targSeqNum := mySeqNum
      outRREP.targAddrMetric := 0 (default) or
                                MIN_METRIC(rte.metricType)

      outRREP.validityTime := (if included) the validity time
                             for route to TargAddr

      if (outRREP.ackReq == TRUE)
      {
         /* include AckReq Message TLV */
      }

      /* Build Address Block */
      AddrBlk := outRREP.origAddr and outRREP.targAddr addresses
           using prefix length information from outRREP.targPrefixLen
           if necessary

      /* TargSeqNum Address Block TLV */
      targSeqNumAddrBlkTlv.value := outRREP.targSeqNum

      /* Build Metric Address Block TLV containing TargAddr metric */
      metricAddrBlkTlv.value := outRREP.targAddrMetric
      if (outRREP.metricType != DEFAULT_METRIC_TYPE)
      { /* include Metric AddrBlkTlv extension byte */
        metricAddrBlkTlv.typeExtension := outRREP.MetricType
      }

      if (outRREP.validityTime is required)
      {
        /* Build VALIDITY_TIME Address Block TLV */
        VALIDITY_TIMEAddrBlkTlv.value = outRREP.validityTime
      }

      Build_RFC_5444_message_header (RREP, 4, IPv4 or IPv6, NN,
                outRREP.hopLimit, outRREQ.hopCount, tlvLength)
      /* unicast RFC 5444 message to rte[OrigAddr].NextHop */
    }

A.3.2. Receive_RREP

    Receive_RREP (inRREP)
    {
      if (inRREP.nbrIP present in blacklist) {
        if (blacklist_expiration_time < current_time)
           return;   /* don't process or regenerate RREQ... */
        else
           remove nbrIP from blacklist;
        }

      if (inRREP does not contain msg_hop_limit, OrigAddr,
                        TargAddr, TargSeqNum, TargAddrMetric)
        return;

      if (inRREP.origAddr and inRREQ.targAddr are not
                        valid routable and unicast addresses)
        return;

      if (inRREP.metricType is present but an unknown value)
        return;
      if (inRREP.targAddrMetric >
                            MAX_METRIC[MetricType] - Cost(Link)
        return;

      /* Extract inRREP values */
      advRte.Address := inRREP.targAddr
      advRte.PrefixLength := inRREP.targPrefixLen f present), or the
        maximum address length for address family of advRte.Address
      advRte.SeqNum := inRREP.targSeqNum
      advRte.MetricType := inRREP.metricType
      advRte.Metric := inRREP.targAddrMetric
      advRte.Cost := inRREP.targAddrMetric + Cost(L) according to
       inRREP's MetricType. L is the link from the advertising router
      advRte.ValidityTime := inRREP.validityTime (if present)
      advRte.NextHopIP := inRREP.nbrIP
      advRte.NextHopIntf := interface the RteMsg was received on
      advRte.HopCount := inRREP.hopCount
      advRte.HopLimit := inRREP.hopLimit (if included)

      rte := Process_Routing_Info (advRte)

      if (inRREP includes AckReq data element)
        Generate_RREP_Ack(inRREP)

      /* update the RteMsgTable and determine if the RREP needs
         to be regenerated */
      regenerate := Update_Rte_Msg_Table(inRREP)

      if (inRREP.targAddr is in the Router Client list)
        send_buffered_packets(rte)    /* start to use the route */
      else if (regenerate)
        Regenerate_RREP(inRREP, rte)
    }





























A.3.3. Regenerate_RREP

    Regenerate_RREP(inRREP, rte)
    {
      if (rte does not exist)
      {
        Generate_RERR(inRREP)
        return;
      }

      outRREP.hopLimit := inRREP.hopLimit - 1
      if (outRREP.hopLimit == 0) /* don't regenerate */
        return;

      if (inRREP.hopCount exists)
      {
        if (inRREP.hopCount >= MAX_HOPCOUNT)
          return; /* don't regenerate */
        outRREP.hopCount := inRREP.hopCount + 1
      }

      /* Marshall parameters */
      /* Include the AckReq when:
         - previous unicast RREP seems not to enable data flow, OR
         - when RREQ is received from same OrigAddr after RREP
              was unicast to rte.nextHop
      */
      outRREP.ackReq := true or false whether to include
            /* if included, set timeout RREP_Ack_SENT_TIMEOUT */
      if (rte.metricType != DEFAULT_METRIC_TYPE)
           outRREP.metricType := rte.metricType
      outRREP.origAddr := inRREP.origAddr
      outRREP.targAddr := rte.Address
      outRREP.targPrefixLen := rte.PrefixLength
                             (if not equal to address length)
      outRREP.targSeqNum := rte.SeqNum
      outRREP.targAddrMetric := rte.Metric
      outRREP.validityTime := (if included) the validity time
                             for route to TargAddr

      outRREP.nextHop := rte.nextHop

      if (outRREP.ackReq == TRUE)
      {
        /* include AckReq Message TLV */
        /* set timeout RREP_Ack_SENT_TIMEOUT */
      }

      /* Build Address Block */
      AddrBlk := {outRREP.origAddr and outRREP.targAddr}
             using prefix length information from
             outRREP.targPrefixLen if necessary

      /* TargSeqNum Address Block TLV */
      targSeqNumAddrBlkTlv.value := outRREP.targSeqNum

      /* Build Metric Address Block TLV containing TargAddrMetric*/
      metricAddrBlkTlv.value := outRREP.targAddrMetric
      if (outRREP.metricType != DEFAULT_METRIC_TYPE)
      { /* include Metric AddrBlkTlv extension byte */
        metricAddrBlkTlv.typeExtension := outRREP.MetricType
      }

      if (outRREP.validityTime is required)
      {
        /* Build VALIDITY_TIME Address Block TLV */
        VALIDITY_TIMEAddrBlkTlv.value := outRREP.validityTime
      }

      Build_RFC_5444_message_header (RREP, 4, IPv4 or IPv6, NN,
                outRREP.hopLimit, 0, tlvLength)
      /* unicast RFC 5444 message to rte[OrigAddr].NextHop */
    }

A.4. Example Algorithms for AODVv2 RERR Operations

RERR message parameters, where RERR can be inRERR or outRERR:

  • RERR.hopLimit := the maximum number of hops this RERR can traverse
  • RERR.pktSource := source IP of unforwardable packet (if present)
  • RERR.metricType := metric type for routes to unreachable destinations
  • RERR.unreachableAddressList[] := addresses of unreachable destinations
  • RERR.prefixLengthList[] := prefix lengths of unreachable destinations
  • RERR.seqNumList[] := sequence numbers for unreachable destinations
  • RERR.intf := the interface on which the RERR was received

A.4.1. Generate_RERR

    Generate_RERR(errorType, triggerPkt, brokenLinkNbrIp)
       /* errorType is either undeliverablePacket or brokenLink */
    {
      switch (errorType)
      {
        case (brokenLink):
             /* a RERR will be required for each MetricType */
        foreach metric type in use
        {
          doGenerate := FALSE
          num-broken-addr := 0
          precursors[] := new empty precursor list
          outRERR.hopLimit := MAX_HOPCOUNT
          outRERR.metricType := the metric type for this loop
          /* find routes which are now Invalid */
          foreach (rte in route table)
          {
            if (brokenLinkNbrIp == rte.nextHop AND
                          rte.MetricType == outRERR.metricType AND
               (rte.State == Active OR
               (rte.State == Idle AND ENABLE_IDLE_IN_RERR)))
            {
               if (rte.State == Active)
               {
                 doGenerate := TRUE
               }
               rte.State := Invalid
               precursors += rte.Precursors (if any)
               outRERR.unreachableAddressList[num-broken-addr] :=
                                                  rte.Address
               outRERR.prefixLengthList[num-broken-addr] :=
                                                  rte.PrefixLength
               outRERR.seqNumList[num-broken-addr] := rte.SeqNum
               num-broken-addr := num-broken-addr + 1
            }
          }
          if (doGenerate == TRUE)
          { /* build and send RFC5444 message as below, then
               repeat loop for other MetricTypes */           }
        }
        case (undeliverablePacket):
          num-broken-addr := 1
          outRERR.hopLimit := MAX_HOPCOUNT
          outRERR.pktSource := triggerPkt.srcIP or
                        triggerPkt.targAddr if packet was a RREP
          /* optional to include outRERR.metricType */
          outRERR.unreachableAddressList[0] := triggerPkt.destIP or
                        triggerPkt.origAddr if packet was a RREP
      }
      if (triggerPkt exists)
      { /* Build PktSource Message TLV */
        pktSourceMessageTlv.value := outRERR.pktSource
      }

      /* The remaining steps add address, prefix length
         and sequence number information for each
         UnreachableAddress, while conforming to the allowed MTU.
         If the MTU is reached, a new message MUST be created. */
      /* Build Address Block */
      AddrBlk := outRERR.unreachableAddressList[]
               using prefix length information from
               outRERR.prefixLengthList[] if necessary

      /* Add SeqNum Address Block TLV including index values */
      seqNumAddrBlkTLV := outRERR.seqNumList[]

      if (outRERR.metricType != DEFAULT_METRIC_TYPE)
      { /* include Metric AddrBlkTlv extension byte */
        metricAddrBlkTlv.typeExtension := outRERR.MetricType
      }

      Build_RFC_5444_message_header (RERR, 4, IPv4 or IPv6, NN,
                outRERR.hopLimit, 0, tlvLength)
      if (undeliverablePacket)
        /* unicast outRERR to rte[outRERR.pktSource].NextHop */
      else if (brokenLink)
        /* unicast to precursors, or multicast to LL-MANET-Routers */
    }

There are two parts to this function, based on whether it was triggered by an undeliverable packet or a broken link to neighboring AODVv2 router.

A.4.2. Receive_RERR

    Receive_RERR (inRERR)
    {
      if (inRERR does not contain msg_hop_limit and at least
                                      one UnreachableAddress)
        return;

      if (inRERR.metricType is present but an unknown value)
        return;

      /* Extract inRERR values, copy relevant UnreachableAddresses,
         their prefix lengths, and sequence numbers to outRERR */
      num-broken-addr := 0;
      precursors[] := new empty list of type precursors/;

      foreach (unreachableAddress in inRERR.unreachableAddressList)
      {
        if (unreachableAddress is not valid routable
                                                and unicast address)
          continue;
        /* find a matching route table entry, assume
                   DEFAULT_METRIC_TYPE if no MetricType included */
        rte := Fetch_Route_Table_Entry (unreachableAddress,
                                           inRERR.metricType)
        if (rte does not exist)
          continue;
        if (rte.State == Invalid)/* ignore already invalid routes */
          continue;
        if (rte.NextHop != inRERR.nbrIP OR
                                rte.NextHopInterface != inRERR.intf)
          continue;
        if (unreachableAddress SeqNum (if known) < rte.SeqNum)
          continue;

        /* keep a note of all precursors of newly Invalid routes */
        precursors += rte.Precursors (if any)

        /* assume prefix length is address length if not included*/
        if (rte.PrefixLength != unreachableAddress prefixLength)
        {
          /* create new route with unreachableAddress information */
          invalidRte := Create_Route_Table_Entry(unreachableAddress,
                unreachableAddress prefixLength,
                unreachableAddress seqNum, inRERR.metricType)
          invalidRte.State := Invalid

          if (rte.PrefixLength > unreachableAddress prefixLength)
            expunge_route(rte);
          rte := invalidRte;
        }
        else if (rte.PrefixLength == unreachableAddress prefixLength)
          rte.State := Invalid;

        outRERR.unreachableAddressList[num-broken-addr] :=rte.Address
        outRERR.prefixLengthList[num-broken-addr] := rte.PrefixLength
        outRERR.seqNumList[num-broken-addr] := rte.SeqNum
        num-broken-addr := num-broken-addr + 1
      }

      if (num-broken-addr)
        Regenerate_RERR(outRERR, inRERR, precursors)
    }





























A.4.3. Regenerate_RERR

    Regenerate_RERR (outRERR, inRERR, precursors)
    {
      /* Marshal parameters */
      outRERR.hopLimit := inRERR.hopLimit - 1
      if (outRERR.hopLimit == 0) /* don't regenerate */
        return;

      outRERR.pktSource := inRERR.pktSource (if included)
      outRERR.metricType := inRERR.MetricType (if included)
                           or DEFAULT_METRIC_TYPE
      /* UnreachableAddressList[], SeqNumList[], and
         PrefixLengthList[] are already up-to-date */

      if (outRERR.pktSource exists)
      {
        /* Build PktSource Message TLV */
        pktSourceMessageTlv.value := outRERR.pktSource
      }
      if (outRERR.metricType != DEFAULT_METRIC_TYPE)
      {
        /* Build MetricType Message TLV */
        metricMsgTlv.value := outRERR.metricType
      }

      /* Build Address Block */
      
      AddrBlk := outRERR.unreachableAddressList[] using prefix length
            information from outRERR.prefixLengthList[] if necessary

      /* Add SeqNum AddressBlock TLV including index values */
      seqNumAddrTLV := outRERR.seqNumList[]

      Build_RFC_5444_message_header (RERR, 4, IPv4 or IPv6, NN,
                outRERR.hopLimit, 0, tlvLength)
      if (outRERR.pktSource exists) {
        /* unicast RFC 5444 message to outRERR.pktSource */
      } else if (number of precursors == 1) {
        /* unicast RFC 5444 message to precursors[0] */
      } else if (number of precursors > 1) {
        /* unicast RFC 5444 message to all precursors, or multicast
           RFC 5444 message to RERR_PRECURSORS if preferable */
      } else {
        /* multicast RFC 5444 message to LL-MANET-Routers */
      }
    }

A.5. Example Algorithms for AODVv2 RREP_Ack Operations

A.5.1. Generate_RREP_Ack

    /* To be sent when RREP includes the AckReq data element */
    Generate_RREP_Ack(inRREP)
    {
      Build_RFC_5444_message_header (RREP_Ack, 4, IPv4 or IPv6, NN,
                1, 0, 0)
      /* unicast RFC 5444 message to inRREP.nbrIP */
    }

A.5.2. Receive_RREP_Ack


    Receive_RREP_Ack(inRREP_Ack)
    {
      /* cancel timeout event for the node sending RREP_Ack */
    }

A.5.3. Timeout_RREP_Ack

    Timeout_RREP_Ack(outRREP)
    {
      /* insert unresponsive node into blacklist */
    }

Appendix B. Changes since revision ...-06.txt

This section lists the changes since AODVv2 revision ...-06.txt

  • Added Victoria Mercieca as co-author.
  • Reorganized protocol message descriptions into major subsections for each protocol message. For protocol messages, organized processing into Generation, Reception, and Regeneration subsections.
  • Separated RREQ and RREP message processing description into separate major subsection which had previously been combined into RteMsg description.
  • Enlarged RREQ Table function to include similar processing for optional flooded RREP messages. The table name has been correspondingly been changed to be the Table for Multicast RteMsgs.
  • Moved sections for Multiple Interfaces and AODVv2 Control Message Generation Limits to be major subsections of the AODVv2 Protocol Operations section.
  • Reorganized the protocol message processing steps into the subsections as previously described, adopting a more step-by-step presentation.
  • Coalesced the router states Broken and Expired into a new combined state named the Invalid state. No changes in processing are required for this.
  • Merged the sections describing Next-hop Router Adjacency Monitoring and Blacklists.
  • Specified that routes created during Route Discovery are marked as Idle routes. If they are used for carrying data they become Active routes.
  • Added Route.LastSeqnum information to route table, so that route activity and sequence number validity can be tracked separately. An active route can still forward traffic even if the sequence number has not been refreshed within MAX_SEQNUM_LIFETIME.
  • Mandated implementation of RREP_Ack as response to AckReq Message TLV in RREP messages. Added field to RREP_Ack to ensure correspondence to the correct AckReq message.
  • Added explanations for what happens if protocol constants are given different values on different AODVv2 routers.
  • Specified that AODVv2 implementations are free to choose their own heuristics for reducing multicast overhead, including RFC 6621.
  • Added appendix to identify AODVv2 requirements from OS implementation of IP and ICMP.
  • Deleted appendix showing example RFC 5444 packet formats.
  • Clarification on the use of RFC 5497 VALIDITY_TIME.
  • In Terminology, deleted superfluous definitions, added missing definitions.
  • Numerous editorial improvements and clarifications.

Appendix C. Changes between revisions 5 and 6

This section lists the changes between AODVv2 revisions ...-05.txt and ...-06.txt.

  • Added Lotte Steenbrink as co-author.
  • Reorganized section on Metrics to improve readability by putting specific topics into subsections.
  • Introduced concept of data element, which is used to clarify the method of enabling RFC 5444 representation for AODVv2 data elements. A list of Data Elements was introduced in section 3, which provides a better understanding of their role than was previously supplied by the table of notational devices.
  • Replaced instances of OrigNode by OrigAddr whenever the more specific meaning is appropriate. Similarly for instances of other node versus address terminology.
  • Introduced concepts of PrefixLengthList and MetricList in order to avoid use of index-based terminology such as OrigNdx and TargNdx.
  • Added section 5, "AODVv2 Message Transmission", describing the intended interface to RFC 5444.
  • Included within the main body of the specification the mandatory setting of the TLV flag thassingleindex for TLVs OrigSeqNum and TargSeqNum.
  • Removed the Route.Timed state. Created a new flag for route table entries known as Route.Timed. This flag can be set when the route is in the active state. Previous description would require that the route table entry be in two states at the same time, which seems to be misleading. The new flag is used to clarify other specification details for Timed routes.
  • Created table 3 to show the correspondence between AODVv2 data elements and RFC 5444 message components.
  • Replaced "invalid" terminology by the more specific terms "broken" or "expired" where appropriate.
  • Eliminated the instance of duplicate specification for inclusion of OrigNode (now, OrigAddr) in the message.
  • Corrected the terminology to be Mid instead of Tail for the trailing address bits of OrigAddr and TargAddr for the example message formats in the appendices.
  • Repaired remaining instances of phraseology that could be construed as indicating that AODV only supports a single network interface.
  • Numerous editorial improvements and clarifications.

Appendix D. Changes from revision ...-04.txt

This section lists the changes between AODVv2 revisions ...-04.txt and ...-05.txt.

  • Normative text moved out of definitions into the relevant section of the body of the specification.
  • Editorial improvements and improvements to consistent terminology were made. Replaced "retransmit" by the slightly more accurate term "regenerate".
  • Issues were resolved as discussed on the mailing list.
  • Changed definition of LoopFree as suggested by Kedar Namjoshi and Richard Trefler to avoid the failure condition that they have described. In order to make understanding easier, replaced abstract parameters R1 by RteMsg and R2 by Route to reduce the level of abstraction when the function LoopFree is discussed.
  • Added text to clarify that different metrics may have different data types and different ranges of acceptable values.
  • Added text to section "RteMsg Structure" to emphasize the proper use of RFC 5444.
  • Included within the main body of the specification the mandatory setting of the TLV flag thassingleindex for TLVs OrigSeqNum and TargSeqNum.
  • Made more extensive use of the AdvRte terminology, in order to better distinguish between the incoming RREQ or RREP message (i.e., RteMsg) versus the route advertised by the RteMsg (i.e., AdvRte).

Appendix E. Changes from revision ...-03.txt

This section lists the changes between AODVv2 revisions ...-03.txt and ...-04.txt.

  • An appendix was added to exhibit algorithmic code for implementation of AODVv2 functions.
  • Numerous editorial improvements and improvements to consistent terminology were made. Terminology related to prefix lengths was made consistent. Some items listed in "Notational Conventions" were no longer used, and so deleted.
  • Issues were resolved as discussed on the mailing list.
  • Appropriate instances of "may" were changed to "MAY".
  • Definition inserted for "upstream".
  • Route.Precursors included as an *optional* route table field
  • Reworded text to avoid use of "relevant".
  • Deleted references to "DestOnly" flag.
  • Refined statements about MetricType TLV to allow for omission when MetricType == HopCount.
  • Bulletized list in section 8.1
  • ENABLE_IDLE_UNREACHABLE renamed to be ENABLE_IDLE_IN_RERR
  • Transmission and subscription to LL-MANET-Routers converted to MUST from SHOULD.

Appendix F. Changes from revision ...-02.txt

This section lists the changes between AODVv2 revisions ...-02.txt and ...-03.txt.

  • The "Added Node" feature was removed. This feature was intended to enable additional routing information to be carried within a RREQ or a RREP message, thus increasing the amount of topological information available to nodes along a routing path. However, enlarging the packet size to include information which might never be used can increase congestion of the wireless medium. The feature can be included as an optional feature at a later date when better algorithms are understood for determining when the inclusion of additional routing information might be worthwhile.
  • Numerous editorial improvements and improvements to consistent terminology were made. Instances of OrigNodeNdx and TargNodeNdx were replaced by OrigNdx and TargNdx, to be consistent with the terminology shown in Table 2.
  • Example RREQ and RREP message formats shown in the Appendices were changed to use OrigSeqNum and TargSeqNum message TLVs instead of using the SeqNum message TLV.
  • Inclusion of the OrigNode's SeqNum in the RREP message is not specified. The processing rules for the OrigNode's SeqNum were incompletely specified in previous versions of the draft, and very little benefit is foreseen for including that information, since reverse path forwarding is used for the RREP.
  • Additional acknowledgements were included, and contributors names were alphabetized.
  • Definitions in the Terminology section capitalize the term to be defined.
  • Uncited bibliographic entries deleted.
  • Ancient "Changes" sections were deleted.

Appendix G. Features of IP needed by AODVv2

AODVv2 needs the following:

  • information that IP routes are requested
  • information that packets are flowing
  • the ability to queue packets.

A reactive protocol reacts when a route is needed. One might say that a route is requested when an application tries to send a packet. The fundamental concept of reactive routing is to avoid creating routes that are not needed, and the way that has been used to know whether a route is needed is when an application tries to send a packet.

If an application tries to send a packet, and the route is not available, the packet has to wait until the route is available.

Appendix H. Multi-homing Considerations

This non-normative information is provided simply to document the results of previous efforts to enable multi-homing. The intention is to simplify the task of future specification if multihoming becomes needed for reactive protocol operation.

Multi-homing is not supported by the AODVv2 specification. There has been previous work indicating that it can be supported by expanding the sequence number to include the AODVv2 router's IP address as a parsable field of the SeqNum. Otherwise, comparing sequence numbers would not work to evaluate freshness. Even when the IP address is included, there isn't a good way to compare sequence numbers from different IP addresses, but at least a handling node can determine whether the two given sequence numbers are comparable. If the route table can store multiple routes for the same destination, then multi-homing can work with sequence numbers augmented by IP addresses.

This non-normative information is provided simply to document the results of previous efforts to enable multi-homing. The intention is to simplify the task of future specification if multihoming becomes needed for reactive protocol operation.

Appendix I. Shifting Network Prefix Advertisement Between AODVv2 Routers

Only one AODVv2 router within a MANET SHOULD be responsible for a particular address at any time. If two AODVv2 routers dynamically shift the advertisement of a network prefix, correct AODVv2 routing behavior must be observed. The AODVv2 router adding the new network prefix must wait for any existing routing information about this network prefix to be purged from the network. Therefore, it must wait at least ROUTER_SEQNUM_AGE_MAX_TIMEOUT after the previous AODVv2 router for this address stopped advertising routing information on its behalf.

Authors' Addresses

Charles E. Perkins Futurewei Inc. 2330 Central Expressway Santa Clara, CA 95050 USA Phone: +1-408-330-4586 EMail: charliep@computer.org
Stan Ratliff Idirect 13861 Sunrise Valley Drive, Suite 300 Herndon, VA 20171 USA EMail: ratliffstan@gmail.com
John Dowdell Airbus Defence and Space Celtic Springs Newport, Wales NP10 8FZ United Kingdom EMail: john.dowdell@airbus.com
Lotte Steenbrink HAW Hamburg, Dept. Informatik Berliner Tor 7 D-20099 Hamburg, Germany EMail: lotte.steenbrink@haw-hamburg.de
Victoria Mercieca Airbus Defence and Space Celtic Springs Newport, Wales NP10 8FZ United Kingdom EMail: victoria.mercieca@airbus.com