Network Working Group T. Clausen Internet-Draft LIX, Ecole Polytechnique, France Intended status: Informational October 27, 2008 Expires: April 30, 2009 The MANET Link Type draft-clausen-manet-linktype-00 Status of This Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 30, 2009. Abstract This document describes the link characteristics and properties for links over which MANET protocols are designed to operate. Clausen Expires April 30, 2009 [Page 1] Internet-Draft MANET Link Type October 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. The MANET Router . . . . . . . . . . . . . . . . . . . . . . . 4 4. MANET Interfaces . . . . . . . . . . . . . . . . . . . . . . . 5 5. MANET Network Dynamics . . . . . . . . . . . . . . . . . . . . 6 6. The MANET Link Type . . . . . . . . . . . . . . . . . . . . . 8 6.1. Connectivity: Symmetry, Transitivity, Continouity ? . . . 8 6.2. Subnet Model and Addresses . . . . . . . . . . . . . . . . 9 6.3. Multicast and Broadcast Scopes . . . . . . . . . . . . . . 10 7. The MANET Addressing Architecture . . . . . . . . . . . . . . 11 7.1. MANET Interface Configuration . . . . . . . . . . . . . . 12 7.2. MANET Addressing Architecture Characteristics . . . . . . 12 8. Security Considerations . . . . . . . . . . . . . . . . . . . 13 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 10. Informative References . . . . . . . . . . . . . . . . . . . . 13 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 14 Clausen Expires April 30, 2009 [Page 2] Internet-Draft MANET Link Type October 2008 1. Introduction A Mobile Ad hoc NETwork, or MANET, is commonly described as a loosely connected set of routers with no predetermined infrastructure and where the routers discover and maintain, even when faced with dynamically changing topologies, a routing structure. Neither the set of routers in the MANET nor their connections to each other can be assumed to be pre-determined nor to be known in advance; either may change randomly over the lifetime of the MANET. MANETs are often constructed from routers using wireless broadcast interfaces, such as IEEE 802.11 interfaces in ad hoc mode, in order to establish connectivity among each other. Other network interfaces and link types, such as Ethernet or point-top-point IP over IP tunnels, are occasionally present between routers in a MANET, and are then also used by MANET protocols, such as a MANET routing protocols (e.g. [RFC3626], [RFC3561], [RFC4728], [RFC3684]) calculating routing paths. This presents MANET protocols with the challenge of operating not only over well known link types such as an Ethernet or a point-to- point IP over IP tunnel, but also to over links as formed over wireless broadcast interfaces. The purpose of this document is to describe a MANET Link Type which accommodates both, such that a protocol designed for the MANET Link Type will operate correctly both when presented with e.g. "an Ethernet" or with "a wireless broadcast interface". 2. Terminology Neighbor - a router B is a neighbor of a router A if B can receive communication directly from router A, without passing through any intermediates at the same layer (i.e. an IP router). Wireless broadcast interface - a network interface where the medium supports true broadcast transmissions, and where link layer messages can be either multicast or unicast. The transmission reachability is constrained by the radio range of the transmittter, which can be time-varying. Node - any device (router or host) that implements IP. Router - a node that forwards IP packets not explicitly addressed to itself. Clausen Expires April 30, 2009 [Page 3] Internet-Draft MANET Link Type October 2008 MANET Router - a router which has, at least, one MANET interface towards a link of the MANET Link Type, as described in this document, and which is capable of ensuring correct operation over that link. Host - any node that is not a router, i.e. a host does not forward packets addressed to others. A Host runs a standard IP stack, and is subject to no MANET Link specific assumptions. MANET Link - a link of the MANET Link type, as described in this document. 3. The MANET Router The entities that are concerned by the MANET Link Type described in this document are MANET routers. A MANET Router is a router which has at least one, but possibly more, MANET interfaces, and zero or more interfaces of other types and towards other networks, as illustrated in Figure 1. \ | / \|/ ------- MANET Interface(s) | +---+----+ | | | Manet | | Router | | | +--------+ | | | | ------- NON-MANET Interface(s) ----+ +---- Figure 1: MANET Router MANET interfaces are the only interfaces which are exposed to links of the MANET Link Type, as described in this document. Protocols operating directly over these MANET interfaces are, therefore, the only protocols which are required to be aware of the characteristics of the MANET Link Type. This entails that protocols which are not intended to operate over MANET interfaces are not required to be able to handle the characteristics of the MANET Link Type. In particular, any node connected to a MANET router over an interface other than a MANET interface, will see the MANET router as it would Clausen Expires April 30, 2009 [Page 4] Internet-Draft MANET Link Type October 2008 see any other IP router. For example, in Figure 2 the hosts connected to the MANET router via the Ethernet link will simply perceive an Ethernet link with hosts and a router, oblivious to if the router is a MANET router or not. \ | / \|/ ------- MANET Interface(s) | +---+----+ | | | Manet | | Router | | | +--------+ | | ------- Ethernet Interface | +-----------------------+ | | | | +---+ +---+ +---+ +---+ | H | | H | | H | | H | +---+ +---+ +---+ +---+ Figure 2: MANET Router with Hosts on an Ethernet Isolated by an IP hop, hosts on the Ethernet link in Figure 2 are not exposed to the particularities of the MANET Link Type - similarly to how, say, hosts on an Ethernet connected to an OSPF router with NBMA interfaces are not exposed to the particularities of the NBMA Link Type. 4. MANET Interfaces An interface is, according to [RFC4862], "a node's attachment to a link", indicating that an interface is a unique point of attachment to a single link. It therefore follows that a MANET interface is a MANET routers point of attachment to a MANET Link. A MANET interface is often a wireless broadcast interface, as illustrated in Figure 3, in which 5 MANET interfaces are connected to the same MANET link and form a simple MANET. If these MANET interfaces are wireless broadcast interfaces, their transmission range is limited, as indicated. Clausen Expires April 30, 2009 [Page 5] Internet-Draft MANET Link Type October 2008 -------+------- ---+------- Transmission ------+------- -------+------- -------+------- Ranges \|/ \|/ \|/ \|/ \|/ | | | | | +-+-+ +-+-+ +-+-+ +-+-+ +-+-+ | A | | B | | C | | D | | E | +---+ +---+ +---+ +---+ +---+ Figure 3: MANET Interface Transmission Ranges In this simple network, a transmission by the node C reaches only nodes B and D on the MANET link, due to the limited transmission range of the wireless broadcast interface. Similarly, a transmission from node B reaches only nodes A and C and a transmission by node D reaches only node E - the latter might be due to environmental interference or obstacles, transmission power levels or antenna properties of node C or D (e.g. directional antennas on either or both of C and D). Note that the "Ethernet-like" interface characteristics that are usually assumed, where all Ethernet interfaces on the same link can reach each other, is a special case of this; and an Ethernet interface would be a perfectly acceptable MANET interface. This example in Figure 3 exhibits some of the characteristics of a MANET Link: connectivity on a link can not be assumed to be symmetric, nor can it be assumed to be transitive. These MANET Link Type characteristics are detailed in Section 6. 5. MANET Network Dynamics In a MANET, the set of participating MANET routers may change, possibly frequently, over time, as can the relative position of the MANET routers change as the network evolves. More specifically, the set of MANET interfaces attached to a given MANET Link may change over time, and a MANET interface may change its position on a MANET Link, which may change the set of neighbors of that MANET interface. The simple network in Figure 3 may evolve over time, as illustrated in Figure 4, where at time t1 node A disappears from the MANET Link and node C and D moves out of radio range from each other and are no longer able to communicate. At time t2, node F appears on the MANET Link, at a position where nodes C and D are within its radio range. The set of MANET interfaces which can be reached by a transmission from any MANET interface on the MANET Link may therefore also change over time. In particular, the ability for a MANET interface to receive a transmission from another MANET interface on the same MANET Clausen Expires April 30, 2009 [Page 6] Internet-Draft MANET Link Type October 2008 Link and at a given point in time does not necessarily indicate that such is also possible in the future. -------+------- ---+------- ------+------- -------+------- -------+------- \|/ \|/ \|/ \|/ \|/ | | | | | +-+-+ +-+-+ +-+-+ +-+-+ +-+-+ t0 | A | | B | | C | | D | | E | +---+ +---+ +---+ +---+ +---+ -------+------- ---+------- ------+------- -------+------- \|/ \|/ \|/ \|/ | | | | +-+-+ +-+-+ +-+-+ +-+-+ t1 | B | | C | | D | | E | +---+ +---+ +---+ +---+ -------+------- ---+------- ------+------- -------+------- -------+------- \|/ \|/ \|/ \|/ \|/ | | | | | +-+-+ +-+-+ +-+-+ +-+-+ +-+-+ t2 | B | | C | | F | | D | | E | +---+ +---+ +---+ +---+ +---+ Figure 4: MANET Network Dynamics Clausen Expires April 30, 2009 [Page 7] Internet-Draft MANET Link Type October 2008 6. The MANET Link Type [Thaler] enumerates a set of properties, which are commonly assumed by applications and upper layer protocols, and notes that these assumptions are becoming increasingly less true. The MANET Link Type is an example of a Link Type which challenges these assumptions. The MANET Link Type characteristics can be summarized as follows: o connectivity can not be assumed to be symmetric within a MANET Link; o connectivity can not be assumed to be transitive within a MANET Link; o connectivity can not be assumed to be continuous within a MANET Link; o the point of attachment to a MANET Link determines the view of that MANET link; o multicast and broadcast can not be assumed to work across a MANET Link; o a subnet is smaller than a MANET Link; o addresses can not be assumed to be part of an on-link subnet on a MANET Link. It is important to note that the MANET Link Type is non-prescriptive, i.e. it does not *require* a link to have these characteristics in order for MANET protocols to operate correctly over it, however protocols designed for the MANET Link Type are *required* to be able to operate correctly also when presented with these link characteristics. This, in particular, entails that for example an Ethernet would be perfectly acceptable as a MANET Link and that MANET protocols would operate correctly when presented with an Ethernet. 6.1. Connectivity: Symmetry, Transitivity, Continouity ? As indicated in Section 4, MANET interfaces on a MANET Link may not all be neighbors, i.e. may not be able to communicate directly between each other without intermediate retransmissions, specifically: Clausen Expires April 30, 2009 [Page 8] Internet-Draft MANET Link Type October 2008 o node A being a neighbor of node B does not necessarily imply that node B is also a neighbor of node A; o node A being a neighbor of nodes B and C does not necessarily imply that nodes B and C are neighbors. Furthermore, as indicated in Section 5, neighbors may change over, specifically: o the ability for a MANET interface to receive a transmission from another MANET interface on the same MANET Link and at a given point in time does not necessarily indicate that such is also possible in the future. 6.2. Subnet Model and Addresses [Thaler] observes that "a subnet is smaller than, or equal to a link", specifically that "destinations with addresses in the same subnet can be reached with TTL (or Hop Count) = 1". On a MANET Link, a transmission with TTL (or Hop Count) = 1 can be received only by MANET interfaces which are neighbors of the sending MANET interface. The first observation is, that "subnet", "reachability without decrementing TTL" and "addresses within a subnet" are intimately related, and assume that "all interfaces with addresses within the same subnet are neighbors". -------+------- ---+------- Transmission ------+------- -------+------- -------+------- Ranges \|/ \|/ \|/ \|/ \|/ | | | | | +-+-+ +-+-+ +-+-+ +-+-+ +-+-+ | A | | B | | C | | D | | E | +---+ +---+ +---+ +---+ +---+ Figure 5: MANET Subnet Challenge Considering node C on the MANET Link as depicted in Figure 5, this router can reach the MANET interfaces of node B and D in a single transmission and with a TTL (or Hop Count) = 1. Nodes B, C and D could, therefore, be candidates for belonging to the same subnet. However a transmission by node B can not reach node D without being retransmitted by node C and so a transmission from node B with a TTL (or Hop Count) = 1 will not reach node D. Furthermore, due to the limited transmission range of node D, node D can reach neither of nodes B and C -- and so, nodes B, C and D can not belong to the same subnet. Clausen Expires April 30, 2009 [Page 9] Internet-Draft MANET Link Type October 2008 This leads to the second observation, that the only set of addresses which on a MANET Link can be guaranteed reachable in a single transmission with TTL (or Hop count) = 1 are those of the transmitting interface. The only addresses which can belong to the same subnet on a MANET Link are, therefore, the addresses assigned to the same MANET interface. While the MANET interfaces of nodes B and C in Figure 5 may not be configured with addresses from within the same subnet, these may still communicate e.g. as point-to-point links where the two endpoints have addresses from unrelated address spaces. 6.3. Multicast and Broadcast Scopes IPv4 Limited Broadcast (255.255.255.255) and IPv4 and IPv6 Link Local Multicast (FFx2::) are specified to not be forwarded [RFC3927] [RFC4291] [RFC3330]. As a consequence, on a MANET Link: o the scope within which a Limited Broadcast or a Link Local Multicast transmission can be received is limited to that of the transmitting MANET interface and its neighbors. In other words, the broadcast and link local multicast scope of a MANET interface on a MANET Link is the MANET interfaces which are within transmission range. In figure Figure 6, the broadcast and multicast scope of node C is, as indicated, the MANET interfaces of nodes B and D; the broadcast and multicast scope of node D is the MANET interface of node E. ---+------- Multicast -------+------- Scopes \|/ \|/ \|/ \|/ \|/ | | | | | +-+-+ +-+-+ +-+-+ +-+-+ +-+-+ | A | | B | | C | | D | | E | +---+ +---+ +---+ +---+ +---+ Figure 6: MANET Broadcast and Multicast Scope Symmetrically, a broadcast or a link local multicast can be received by any MANET interface within transmission range of the transmitter, whether those are the receivers intended or not. Due to the fact that connectivity can not be assumed to be symmetric, the transmitter may not a priori know which MANET interfaces have received the broadcast or link local multicast, nor can it be assumed that the recipients a posteriori can signal that they received the broadcast or link local multicast. Clausen Expires April 30, 2009 [Page 10] Internet-Draft MANET Link Type October 2008 7. The MANET Addressing Architecture This section presents an addressing architecture model for MANETs, which preserves the integrity of the conventional IP addressing architecture while allowing for the particularities of the MANET Link Type. In particular, the applications and protocols running on hosts are not exposed to a MANET Link. Only MANET interfaces of MANET routers are required to be aware of the MANET Link Type, and to be configured according to the characteristics of the MANET Link Type. A MANET router is a router with at least one MANET interface towards a MANET Link and, possibly, with zero or more other interfaces towards other routers or hosts. The MANET router may, as any router be delegated zero or more prefixes, which it may assign, integrally or as subnet prefixes, to any links of its non-MANET interfaces, which are configured accordingly. Hosts and routers on these non- MANET interfaces may be assigned addresses from within these prefixes according to the address (auto)configuration mechanisms governing these (non-MANET) links, such as [RFC4862] and [RFC2131]. Considering the example in Figure 7, the MANET router is delegated the prefix p::/48. Subnet-prefixes p:1::/62, p:2::/62 and p:3::/63 from p::/48 are derived and assigned to the non-MANET links. Interfaces on these links are configured with addresses from within the subnet prefix of that link, as usual. M A \ | / N \|/ ------- MANET Interface(s) E | T +- --+--- -+ | | Manet | p::/48 .........................| Router |.............................. | | +- ------ -+ N p:1::/62 | | | p:3::/62 o +-------+-------+-------+ | +-------+-------+-------+ n | | | | | | | | | | +---+ +---+ +---+ +---+ | +---+ +---+ +---+ +---+ M | H | | H | | H | | H | | | H | | H | | H | | H | A +---+ +---+ +---+ +---+ | +---+ +---+ +---+ +---+ N | E -------------+---------------- T p:2::/62 Clausen Expires April 30, 2009 [Page 11] Internet-Draft MANET Link Type October 2008 Figure 7: MANET Router and Prefixes Example The configuration of MANET interface(s) of the MANET router requires special attention, and is detailed in Section 7.1. 7.1. MANET Interface Configuration As described in Section 6.2, on a MANET Link the only addresses which can be guaranteed to be reachable with TTL (or Hop Count) = 1, and therefore can be admitted to be within the same subnet, are the addresses assigned to the sending MANET interface. Consequently, MANET interfaces must be configured such that: o no two MANET interfaces appear within the same subnet, i.e. with the same prefix and prefix length. This can be, and is commonly, accomplished by configuring MANET interfaces with a /32 (IPv4) or a /128 (IPv6) address, e.g. as an unnumbered interface, borrowing a single IP address from a non-MANET interface of the MANET router. It is worth noting that prefix lengths shorter than /128 (IPv6) or /32 (IPv4) are possible on MANET interfaces, as long as the prefixes are unique to a single MANET interface. Note that the above statements are not an exception, but simply a clarification that MANET are no different from other networks in this respect. 7.2. MANET Addressing Architecture Characteristics The MANET addressing architecture presented in this section makes a clear separation between the role of MANET router and host in a MANET, recognizing that: o MANET Link Type characteristics are only exposed to MANET interfaces of MANET-aware routers, running appropriate protocols; o routers and hosts, and more generally networks/subnets, on non- MANET interface(s) are not subject to the particularities of the MANET Link Type but are isolated herefrom by an IP hop; o applications and protocols on hosts and routers, and more generally networks/subnets, on non-MANET interfaces run unmodified. Note that this addressing architecture is similar to how routing in the existing Internet is structured. Routers run their routing protocol over router interconnects with various characteristics to which only the routing protocols are privy. On the other hand, hosts Clausen Expires April 30, 2009 [Page 12] Internet-Draft MANET Link Type October 2008 connect to routers over interfaces with well-defined characteristics. 8. Security Considerations This document does not currently present any security considerations. 9. IANA Considerations This document does not have any IANA actions 10. Informative References [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [RFC3330] IANA, IANA., "Special-Use IPv4 Addresses", RFC 3330, September 2002. [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- Demand Distance Vector (AODV) Routing", RFC 3561, July 2003. [RFC3626] Clausen, T. and P. Jacquet, "The Optimized Link State Routing Protocol", RFC 3626, October 2003. [RFC3684] Ogier, R., Templin, f., and M. Lewis, "Topology Dissemination Based on Reverse-Path Forwarding", RFC 3684, February 2004. [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. [RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic Configuration of IPv4 Link-Local Addresses", RFC 3927, May 2005. [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. [RFC4862] Narten, T., Thomson, S., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, September 2007. [Thaler] Thaler, D., "Evolution of the IP Model", Work In Progress draft-thaler-ip-model-evolution-01.txt, July 2008. Clausen Expires April 30, 2009 [Page 13] Internet-Draft MANET Link Type October 2008 Appendix A. Acknowledgments This document is greatly inspired from discussions with Dave Thaler (Microsoft), Jari Arkko (Ericsson), Mark Townsley (Cisco), Ian Chakeres (Motorola). Christopher Dearlove (BAE Systems) and Emmanuel Baccelli (INRIA) both provided reviews and insightful comments on early iterations of this text. Author's Address Thomas Heide Clausen LIX, Ecole Polytechnique, France Phone: +33 6 6058 9349 EMail: T.Clausen@computer.org URI: http://www.thomasclausen.org/ Clausen Expires April 30, 2009 [Page 14] Internet-Draft MANET Link Type October 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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