Fast failure detection in VRRP with Point to Point BFDCisco Systems, Inc.3265 CISCO WaySan Jose95134United States+91 80 4429 2530nitisgup@cisco.comhttp://www.cisco.com/Cisco Systems, Inc.Sarjapur Outer Ring RoadBangalore560103India+91 80 4429 2166addogra@cisco.comhttp://www.cisco.com/23 The MaltingsHaddingtonScotlandEH414EFUnited Kingdomietf@doch.org.ukIndividualgregimirsky@gmail.comIndividualjefftant.ietf@gmail.com
General
RFCVRRPBFDPeer learning
This document describes how Point to Point Bidirectional Forwarding Detection (BFD) can be used to support sub-second detection of a Master Router failure in the Virtual Router Redundancy Protocol (VRRP).
The Virtual Router Redundancy Protocol (VRRP) provides redundant Virtual gateways in the Local Area Network (LAN), which is typically the first point of failure for end-hosts sending traffic out of the LAN. Fast failure detection of VRRP Master is critical in supporting high availability of services and improved Quality of Experience to users.
In VRRP specification, Backup routers depend on VRRP packets generated at a regular interval by the Master router, to detect the health of the VRRP Master. Faster failure detection can be achieved within VRRP protocol by reducing the Advertisement and Master Down Interval. However, sub second Advert timers, can put extra load on CPU and the network bandwidth which may not be desirable.
Since the VRRP protocol depends on the availability of Layer 3 IPv4 or IPv6 connectivity between redundant peers, the VRRP protocol can interact with the Layer 3 variant of BFD as described in to achieve a much faster failure detection of the VRRP Master on the LAN. BFD, as specified by the can provide a much faster failure detection in the range of 150ms, if implemented in the part of a Network device which scales better than VRRP when sub second Advert timers are used.
In this document, several words are used to signify the requirements of the specification. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.
BFD for IPv4 or IPv6 (Single Hop) requires that in order for a BFD session to be formed both peers participating in a BFD session need to know its peer IPv4 or IPV6 address. This poses a unique problem with the definition of the VRRP protocol, that makes the use of BFD for IPv4 or IPv6 more challenging. In VRRP it is only the Master router that sends Advert packets. This means that a Master router is not aware of any Backup routers, and Backup routers are only aware of the Master router. This also means that a Backup router is not aware of any other Backup routers in the Network.
Since BFD for IPv4 or IPv6 requires that a session be formed by both peers using a full destination and source address, there needs to be some external means to provide this information to BFD on behalf of VRRP. Once the peer information is made available, VRRP can form BFD sessions with its peer Virtual Router. The BFD session for a given Virtual Router is identified as the Critical Path BFD Session, which is the session that forms between the current VRRP Master router, and the highest priority Backup router. When the Critical Path BFD Session identified by VRRP as having changed state from Up to Down, then this will be interpreted by the VRRP state machine on the highest priority Backup router as a Master Down event. A Master Down event means that the highest priority Backup peer will immediately become the new Master for the Virtual Router.NOTE: At all times, the normal fail-over mechanism defined in the VRRP will be unaffected, and the BFD fail-over mechanism will always resort to normal VRRP fail-over.
This draft defines the mechanism used by the VRRP protocol to build a peer table that will help in forming of BFD session and the detection of Critical Path BFD session. If the Critical Path BFD session were to go down, it will signal a Master Down event and make the most preferred Backup router as the VRRP Master router. This requires an extension to the VRRP protocol.
This can be achieved by defining a new type in the VRRP Advert packet, and allowing VRRP peers to build a peer table in any of the operational state, Master or Backup.
In this mode of operation VRRP peers learn the adjacent routers, and form BFD session between the learnt routers. In order to build the peer table, all routers send VRRP Advert packets whilst in any of the operational states (Master or Backup). Normally VRRP peers only send Advert packets whilst in the Master state, however in this mode VRRP Backup peers will also send Advert packets with the type field set to BACKUP ADVERTISEMENT type defined in of this document. The VRRP Master router will still continue to send packets with the Advert type as ADVERTISEMENT as defined in the VRRP protocol. This is to maintain inter-operability with peers complying to VRRP protocol.
Additionally, Advert packets sent from Backup Peers must not use the Virtual router MAC address as the source address. Instead it must use the Interface MAC address as the source address from which the packet is sent from. This is because the source MAC override feature is used by the Master to send Advert packets from the Virtual Router MAC address, which is used to keep the bridging cache on LAN switches and bridging devices refreshed with the destination port for the Virtual Router MAC.
VRRP peers can now form the peer table by learning the source address in the ADVERTISEMENT or BACKUP ADVERTISEMENT packet sent by VRRP Master or Backup peers. This allows peers to create BFD sessions with other operational peers.
A peer entry should be removed from the peer table if Advert is not
received from a peer for a period of (3 * the Advert interval).
In the above configuration there are three routers on the LAN protecting an IPv4 or IPv6 address associated to a Virtual Router ID 1. Rtr1 is the Master router since it has the highest priority compared to Rtr2 and Rtr3. Now if peer learning extension is enabled on all the peers. Rtr1 will send the Advert packet with type field set to 1. While Rtr2 and Rtr3 will send the Advert packet with type field set to 2. In the above configuration the peer table built at each router is shown below:Once the peer tables are formed, VRRP on each router can form a BFD sessions with the learnt peers.The Critical BFD Session is determined to be the session between the VRRP Master and the next best VRRP Backup.
Failure of the Critical BFD session indicates that the Master is no longer available and the most preferred Backup will now become Master.
In the above example the Critical BFD session is shared between Rtr1 and Rtr2. If the BFD Session goes from Up to Down state, Rtr2 can treat it as a Master down event and immediately assume the role of VRRP Master router for VRID 1 and Rtr3 will become the critical Backup. If the priorities of two Backup routers are same then the primary IPvX Address of the sender is used to determine the highest priority Backup. Where higher IPvX address has higher priority.
Following parameters are added to the VRRP protocol to support this mode of operation.
Following timers are added to the VRRP protocol to support this mode of operation.
Following State Machine replaces the state Machine outlined in section 6.4 of the VRRP protocol to support this mode of operation.
Please refer to the section 6.4 of for State description.
Following state machine replaces the state machine outlined in section 6.4.1 of Following state machine replaces the state machine outlined in section 6.4.2 of Following state machine replaces the state machine outlined in section 6.4.3 of
To reduce the number of packets generated at a regular interval, Backup Advert packets may be sent at a reduced rate as compared to Advert packets sent by the VRRP Master.
A VRRP peer that forms a member of this Virtual Router, but does not support this feature or extension
must be configured with the lowest priority, and will only operate as the Router of last resort on failure of all other VRRP routers supporting this functionality.
It is recommended that mechanism defined by this draft, to interface VRRP with BFD should be used when BFD can support more aggressive monitoring timers than VRRP. Otherwise it is desirable not to interface VRRP with BFD for determining the health of VRRP Master.
This Draft does not preclude the possibility of the peer table being
populated by means of manual configuration, instead of using the
BACKUP ADVERTISEMENT as defined by the Draft.
This document requests IANA to create a new name space that is to be managed by IANA. The document defines a new VRRP Packet Type. The VRRP Packet Types are discussed below.This document defines in Section 3.3 a "BACKUP ADVERTISEMENT" VRRP Packet Type.
The new name space has to be created by the IANA and they will maintain this new name space.
The field for this namespace is 4-Bits, and IANA guidelines for assignments for this
field are as follows:
Future allocations of values in this name space are to be assigned by
IANA using the "Specification Required" policy defined in
Security considerations discussed in , , apply to this document. There are no additional security considerations identified by this draft. The authors gratefully acknowledge the contributions of Gerry Meyer, and Mouli Chandramouli, for their contributions to the draft. The authors will also like to thank Jeffrey Haas, Maik Pfeil, Chris Bowers and Vengada Prasad Govindan for their comments and suggestions.Bidirectional Forwarding Detection (BFD)Juniper NetworksJuniper Network
BFD Working Group
Internet Engineering Task ForceThis document describes a protocol intended to detect faults in the
bidirectional path between two forwarding engines, including
interfaces, data link(s), and to the extent possible the forwarding
engines themselves, with potentially very low latency. It operates
independently of media, data protocols, and routing protocols.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.Key words for use in RFCs to Indicate Requirement LevelsHarvard University
Network Working Group
Internet Engineering Task ForceThis document describes a protocol intended to detect faults in the
bidirectional path between two forwarding engines, including
interfaces, data link(s), and to the extent possible the forwarding
engines themselves, with potentially very low latency. It operates
independently of media, data protocols, and routing protocols.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.Bidirectional Forwarding Detection (BFD) for IPv4 and IPv6 (Single Hop)Juniper NetworksJuniper Network
BFD Working Group
Internet Engineering Task Force This document describes the use of the Bidirectional Forwarding
Detection (BFD) protocol over IPv4 and IPv6 for single IP hops.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.Virtual Router Redundancy Protocol (VRRP) Version 3 for IPv4 and IPv6Ericsson
VRRP Working Group
Internet Engineering Task Force
This memo defines the Virtual Router Redundancy Protocol (VRRP) for
IPv4 and IPv6. It is version three (3) of the protocol, and it is
based on VRRP (version 2) for IPv4 that is defined in RFC 3768 and in
"Virtual Router Redundancy Protocol for IPv6". VRRP specifies an
election protocol that dynamically assigns responsibility for a
virtual router to one of the VRRP routers on a LAN. The VRRP router
controlling the IPv4 or IPv6 address(es) associated with a virtual
router is called the Master, and it forwards packets sent to these
IPv4 or IPv6 addresses. VRRP Master routers are configured with
virtual IPv4 or IPv6 addresses, and VRRP Backup routers infer the
address family of the virtual addresses being carried based on the
transport protocol. Within a VRRP router, the virtual routers in
each of the IPv4 and IPv6 address families are a domain unto
themselves and do not overlap. The election process provides dynamic
failover in the forwarding responsibility should the Master become
unavailable. For IPv4, the advantage gained from using VRRP is a
higher-availability default path without requiring configuration of
dynamic routing or router discovery protocols on every end-host. For
IPv6, the advantage gained from using VRRP for IPv6 is a quicker
switchover to Backup routers than can be obtained with standard IPv6
Neighbor Discovery mechanisms.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.Guidelines for Writing an IANA Considerations Section in RFCsIBM CorporationMaxware
Network Working Group
Internet Engineering Task ForceMany protocols make use of identifiers consisting of constants and
other well-known values. Even after a protocol has been defined and
deployment has begun, new values may need to be assigned (e.g., for a
new option type in DHCP, or a new encryption or authentication
algorithm for IPSec). To insure that such quantities have consistent
values and interpretations in different implementations, their
assignment must be administered by a central authority. For IETF
protocols, that role is provided by the Internet Assigned Numbers
Authority (IANA).
In order for the IANA to manage a given name space prudently, it
needs guidelines describing the conditions under which new values can
be assigned. If the IANA is expected to play a role in the management
of a name space, the IANA must be given clear and concise
instructions describing that role. This document discusses issues
that should be considered in formulating a policy for assigning
values to a name space and provides guidelines to document authors on
the specific text that must be included in documents that place
demands on the IANA.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.