2.5.1 Bidirectional Forwarding Detection (bfd)

NOTE: This charter is a snapshot of the 62nd IETF Meeting in Minneapolis, MN USA. It may now be out-of-date.

Last Modified: 2005-02-09

Chair(s):

David Ward <dward@cisco.com>
Jeffrey Haas <jhaas@nexthop.com>

Routing Area Director(s):

Bill Fenner <fenner@research.att.com>
Alex Zinin <zinin@psg.com>

Routing Area Advisor:

Alex Zinin <zinin@psg.com>

Technical Advisor(s):

Dave Katz <dkatz@juniper.net>

Mailing Lists:

General Discussion: rtg-bfd@ietf.org
To Subscribe: rtg-bfd-request@ietf.org
In Body: With a subject line: subscribe
Archive: ftp://ftp.ietf.org/ietf-mail-archive/rtg-bfd/

Description of Working Group:

The BFD Working Group is chartered to specify a protocol for
bidirectional forwarding detection (BFD), as well as extensions to be
used within the scope of BFD and IP routing, or protocols such as MPLS
that are based on IP routing, in a way that will encourage multiple,
inter-operable vendor implementations.

BFD is a protocol intended to detect faults in the bidirectional path
between two forwarding engines, including physical interfaces,
subinterfaces, 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. An
additional goal is to provide a single mechanism that can be used for
liveness detection over any media, at any protocol layer, with
a wide range of detection times and overhead, to avoid a proliferation
of different methods.

Important characteristics of BFD include:

- Simple, fixed-field encoding to facilitate implementations in
hardware

- Independence of the data protocol being forwarded between two
systems.
  BFD packets are carried as the payload of whatever encapsulating
  protocol is appropriate for the medium and network.

- Path independence: BFD can provide failure detection on any kind of
  path between systems, including direct physical links, virtual
  circuits, tunnels, MPLS LSPs, multihop routed paths, and
  unidirectional links (so long as there is some return path, of
  course.)

- Ability to be bootstrapped by any other protocol that automatically
  forms peer, neighbor or adjacency relationships to seed BFD endpoint
  discovery.

At this time the WG is chartered to complete the following work items
(additional items will require rechartering):

1. Develop the base BFD protocol specification and submit it to the
IESG
  for publication as a Proposed Standard
                                                                     
  2. Document BFD encapsulation and usage profile for single-hop IPv4
  and IPv6 adjacencies (e.g, physical links and IP/GRE tunnels for
  static routes, IS-IS, OSPFv2, OSPFv3, single-hop BGP) and submit the
  specification to the IESG for publication as a Proposed Standard.
                                                                     
3. Document BFD encapsulation and usage profile for MPLS LSPs and
submit
  the specification to the IESG for publication as a Proposed
Standard.
                                                                     
                                                                     

 
4. Develop the MIB module for BFD and submit it to the IESG for
  publication as a Proposed Standard.
                                                                     
5. Document BFD encapsulation and usage profile for multi-hop IPv4
  and IPv6 adjacencies (e.g. OSPF virtual links and iBGP sessions)
  and submit the specification to the IESG for publication as a
  Proposed Standard.

Topics for Possible Future Work:

1. Document BFD directly over 802.3 in close collaboration and
  synchronization with the IEEE.

Goals and Milestones:

Aug 04  Submit the base protocol specification to the IESG to be considered as a Proposed Standard.
Aug 04  Submit BFD encapsulation and usage profile for single-hop IPv4 and IPv6 adjacencies to the IESG to be considered as a Proposed Standard
Aug 04  Submit BFD encapsulation and usage profile for MPLS LSPs to the IESG to be considered as a Proposed Standard
Nov 04  Submit BFD MIB to the IESG to be considered as Proposed Standard.
Feb 05  Submit BFD encapsulation and usage profile for multi-hop IPv4 and IPv6 adjacencies to the IESG to be considered as a Proposed Standard

Internet-Drafts:

  • draft-ietf-bfd-mpls-01.txt
  • draft-ietf-bfd-base-01.txt
  • draft-ietf-bfd-multihop-01.txt
  • draft-ietf-bfd-v4v6-1hop-01.txt

    No Request For Comments

    Current Meeting Report
    BFD Working Group minutes
    IETF 62
    Chairs: Dave Ward, Jeff Haas

    Updates on the specifications, Dave Ward
    ------
    A new state machine has been added.
    Added support for SHA-1 authentication
    Added text clarifying what IGPs should do during a Graceful Restart
    Responded and incorporated all comments and inquiries on the base list
    Generic bootstrap document will be written and should become a working group draft.

    Added 2 diagnostic codes dealing with concatenated path down.
    Note that bfd session isn't taken down in this case.

    Security changes:
    Added support for SHA-1.
    Removed requirement to drop session when changing authentication.

    Introduced incompatible state machine change, we're now BFD version 1.
    Protocol now carries the state that the remote state machine is in.
    The protocol no longer has an "I hear you" bit.

    [Discussion about potential protocol expansion issues. Answer, we still have a reserved bit.]

    Version 1 will become the default version of the protocol
    Version 0 is not widely deployed, so this shouldn't be an issue.

    BFD IS-IS interaction
    For details, see IS-IS WG

    New drafts will be out shortly after IETF

    Review period of 3 weeks on the draft.
    WG last call 3 weeks after that.

    Discussion:
    Pekka: TTL 255 removed?
    Dave W: When running authentication, don't need to verify TTL
    Pekka: We want to do the TTL check first to protect against attacks on the authentication system.
    Dave W: It can be configured on.
    Pekka: It should say it must be configured.
    Dave K: If your implementation can't handle bad authentication packets [at line rate], your implementation [has problems].
    Pekka: [Concern about authentication to be used as an attack on the control plane]
    Dave W: You can still configure the TTL 255 check
    Pekka: If you're running without authentication, you *must* use the TTL check
    Jeff: Show of hands in the room, should we require the TTL check when using authentication [yes]
    Dave K: There are known situations when the TTL check is known broken. E.g. the implementation decrements the TTL internally.
    Jeff: There appears to be some consensus that the TTL should be a SHOULD, instead of a MAY; not a must.
    [?] - Default Configuration parameters as part of the spec?
    Dave K: Configuration parameters don't belong in the spec
    Dave W: [?]
    Dave K: SHOULD works for me

    Working group procedural status, Jeff
    -----
    We're late on our deliverables.

    The WG was reminded of our charter to create a protocol to detect forwarding plane liveness. This is a very tightly focused WG meant to address a generic solution on a number of media. Solutions for specific problems on given media are likely out of scope.


    Slides

    BFD protocol update
    Bidrectional Forwarding Detection