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Transparent Interconnection of Lots of Links (TRILL): Bidirectional Forwarding Detection (BFD) Support

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7175.
Authors Vishwas Manral , Donald E. Eastlake 3rd , David Ward , Ayan Banerjee
Last updated 2018-12-20 (Latest revision 2012-07-16)
Replaces draft-manral-trill-bfd-encaps
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd (None)
IESG IESG state Became RFC 7175 (Proposed Standard)
Action Holders
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD Ralph Droms
IESG note
Send notices to (None)
TRILL Working Group                                            V. Manral
INTERNET-DRAFT                                       Hewlett Packard Co.
Intended status: Proposed Standard                           D. Eastlake
                                                          Huawei R&D USA
                                                                 D. Ward
                                                           Cisco Systems
                                                             A. Banerjee
                                                        Cumulus Networks
Expires: January 15, 2013                                  July 16, 2012

          TRILL (Transparent Interconnetion of Lots of Links):
            Bidirectional Forwarding Detection (BFD) Support


   This document specifies use of the BFD (Bidirectional Forwarding
   Detection) protocol in RBridge campuses based on the Rbridge Channel
   extension to the the TRILL (TRansparent Interconnection of Lots of
   Links) protocol.

   BFD is a widely deployed OAM (Operations, Administration, and
   Maintenance) mechanism in IP and MPLS (Multi Protocol Label
   Switching) networks, using UDP and ACH (Associated Channel Header)
   encapsulation respectively.  This document specifies the BFD
   encapsulation over TRILL.

Status of This Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.  Distribution of this document is
   unlimited. Comments should be sent to the TRILL working group mailing
   list: <>.

   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-

   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."

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   The list of current Internet-Drafts can be accessed at The list of Internet-Draft
   Shadow Directories can be accessed at

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Table of Contents

      1. Introduction............................................4
      1.1 Terminology............................................4

      2.  BFD over TRILL.........................................6
      2.1 Sessions and Initialization............................6

      3. TRILL BFD Control Protocol..............................8
      3.1 One-Hop TRILL BFD Control..............................8
      3.2 BFD Control Frame Processing...........................8

      4. TRILL BFD Echo Protocol.................................9
      4.1  BFD Echo Frame Processing.............................9

      5. Management and Operations Considerations...............11
      6. Default Authentication.................................12
      7. Security Considerations................................14
      8. IANA Considerations....................................15
      9. Acknowledgements.......................................15
      Normative References......................................16
      Informative References....................................16
      Recent Changes Record.....................................18

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1. Introduction

   Faster convergence is a critical feature of TRILL (Transparent
   Interconnection of Lots of Links [RFC6325]) networks.  The TRILL IS-
   IS Hellos [RFC6327] [IS-IS] used between RBridges provide a basic
   neighbor and continuity check for TRILL links.  However, failure
   detection by non- receipt of such Hellos is based on the holding time
   parameter that is commonly set to a value of tens of seconds and, in
   any case, has a minimum expressible value of one second.

   Some applications, including voice over IP, may wish, with high
   probability, to detect interruptions in continuity within a much
   shorter time period.  In some cases physical layer failures can be
   detected very rapidly but this is not always possible, such as when
   there is a failure between two bridges that are in turn between two
   RBridges.  There are also many subtle failures possible at higher
   levels.  For example, some forms of failure could affect unicast
   frames while still letting multicast frames through; since all TRILL
   IS-IS Hellos are multicast such a failure cannot be detected with
   Hellos.  Thus, a low overhead method for frequently testing
   continuity for the TRILL Data between neighbor RBridges is necessary
   for some applications.  The BFD (Bi-directional Forwarding Detection
   [RFC5880]) protocol provides a low-overhead method for the rapid
   detection of connectivity failures.

   BFD is a widely deployed OAM (Operations, Administration, and
   Maintenance, [RFC6291]) mechanism in IP and MPLS (Multi Protocol
   Label Switching) networks, using UDP and ACH (Associated Channel
   Header) encapsulation respectively. This document describes a TRILL
   encapsulation for BFD packets for networks that forward based on the
   TRILL Header.

1.1 Terminology

   This document uses the acronyms defined in [RFC6325] along with the

      BFD: Bi-directional Forwarding Detection

      IP: Internet Protocol

      IS-IS: Intermediate-System to Intermediate-System

      MH: Multi-Hop

      PPP: Point-to-Point Protocol

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      OAM: Operations, Administration, and Maintenance

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

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2.  BFD over TRILL

   TRILL supports unicast neighbor BFD Echo and one-hop and multi-hop
   BFD Control, as specified below, over the Rbridge Channel facility
   [TRILLChannel].  (Multi-destination BFD is a work in progress
   [MultiBFD].) BFD over TRILL support is similar to BFD over IP support
   [RFC5881] except where differences are explicitly mentioned.

   Asynchronous and demand modes MUST BE supported [RFC5880].  BFD over
   TRILL supports the Echo function, however implementation of TRILL BFD
   Echo is optional and it can only be used for single-hop sessions.

   The TRILL Header hop count in the BFD packets is sent out with the
   maximum value of 0x3F.  To prevent spoofing attacks, the TRILL hop
   count of a received session is checked [RFC5082].  For a single-hop
   session if the hop count is less than 0x3F and the Rbridge Channel
   Header MH flag is zero, the packet is discarded.  For multihop
   sessions the hop count check can be disabled if the MH flag is one.

   As in BFD for IP the format of the Echo Packet content is not

   New Rbridge Channel code points for BFD TRILL Control and BFD Echo
   packets are specified.

   Authentication mechanisms as supported in BFD are also supported for
   BFD running over TRILL.

2.1 Sessions and Initialization

   Within an RBridge campus, there will be no more than one TRILL BFD
   Control session from any RBridge RB1 to RBridge RB2 for each RB1
   TRILL port.  This BFD session must be bound to this interface.  As
   such, both sides of a session MUST take the "Active" role (sending
   initial BFD Control packets with a zero value of Your Discriminator),
   and any BFD packet from the remote machine with a zero value of Your
   Discriminator MUST be associated with the session bound to the remote
   system and interface.

   Note that TRILL BFD provides OAM facilities for the TRILL data plane.
   This is above whatever protocol is in use on a particular link, such
   as a PPP [RFC6361] link or an Ethernet link [RFC6325].  Link
   technology specific OAM protocols may be used on a link between
   neighbor RBridges, for example Continuity Fault Management [802.1Q]
   if the link is Ethernet.  But such link layer OAM and coordination
   between it and TRILL data plane layer OAM, such as TRILL BFD, is
   beyond the scope of this document.

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   If lower level mechanisms, such as link aggregation [802.1AX], are in
   use that present a single logical interface to TRILL IS-IS, only a
   single TRILL BFD session can be established to any other RBridge over
   this logical interface.  However, lower layer OAM could be aware of
   and/or run separately on each of the components of an aggregation.

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3. TRILL BFD Control Protocol

   TRILL BFD Control frames are unicast TRILL Rbridge Channel frames
   [TRILLChannel].  The Rbridge Channel Protocol value is given in
   Section 8. The protocol specific data associated with the TRILL BFD
   Control protocol is as shown in Section 4.1 of [RFC5880].

3.1 One-Hop TRILL BFD Control

   One-hop TRILL BFD Control is typically used to rapidly detect link
   and RBridge failures.  TRILL BFD frames over one hop for such
   purposes SHOULD be sent with high priority; that is, the Inner.VLAN
   tag priority should be 7, they should be queued for transmission as
   maximum priority frames and, if they are being sent on an Ethernet
   link where the output port is configured to include an Outer.VLAN
   tag, that tag should specify priority 7.

   For neighbor RBridges RB1 and RB2, each RBridge sends one-hop TRILL
   BFD Control frames to the other only if TRILL IS-IS has detected bi-
   directional connectivity, that is, the adjacency is in the Two-Way or
   Report state [RFC6327] and both RBridges indicate support of TRILL
   BFD is enabled.  The BFD Enabled TLV is used to indicate this as
   specified in [RFC6213].

3.2 BFD Control Frame Processing

   The following tests SHOULD be performed on received TRILL BFD Control
   frames before generic BFD processing.

   Is the M-bit in the TRILL Header non-zero?  If so, discard the frame.
   (Multi-destination BFD is a work in progress [MultiBFD].)  Failure to
   perform this test would make a denial-of-service attack using bogus
   multi-destination BFD Control frames easier.

   If the Channel Header MH flag is zero, indicating one-hop, test that
   the TRILL Header hop count received was 0x3F (i.e., is 0x3E if it has
   already been decremented) and if it is any other value discard the
   frame.  If the MH Channel flag is one, indicating multi-hop, test
   that the TRILL Header hop count received was not less than a
   configurable value that defaults to 0x30.  If it is less, discard the
   frame.  Failure to perform these tests would make it easier to spoof
   BFD Control frames. However, if forged BFD Control frames are a
   concern, then BFD Authentication [RFC5880] should be used.

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4. TRILL BFD Echo Protocol

   A TRILL BFD Echo frame is a unicast Rbridge Channel frame, as
   specified in [TRILLChannel], which should be forwarded back by an
   immediate neighbor because both the ingress and egress nicknames are
   set to a nickname of the originating RBridge.  Normal TRILL Data
   frame forwarding will cause the frame to be returned unless micro-
   loop suppression logic in the neighbor RBrdge prohibits sending a
   frame back out the port on which it was received or the like.
   RBridges with such prohibitions cannot support BFD Echo.  The TRILL
   OAM protocol number for BFD Echo is given in Section 8.

   TRILL BFD Echo frames SHOULD be sent on a link only if the following
   conditions are met. An Echo originated under other circumstances will
   consume bandwidth and CPU resources but is unlikely to be returned.

    - A TRILL BFD Control session has been established,

    - TRILL BFD Echo support is indicated by the potentially echo
      responding RBridge,

    - The adjacency is in the Report state [RFC6327], and

    - The TRILL BFD Echo originating RBridge wishes to make use of this
      optional feature.

   Since the originating RBridge is the RBridge that will be processing
   a returned Echo frame, the entire TRILL BFD Echo protocol specific
   data area is considered opaque and left to the discretion of the
   originating RBridge.  Nevertheless, it is suggested that this data
   include information by which the originating RBridge can authenticate
   the returned BFD Echo frame and confirm the neighbor that echoed the
   frame back.  For example, it could include its own SystemID, the
   neighbor's SystemID, a session identifier and a sequence count as
   well as a Message Authentication Code.

4.1  BFD Echo Frame Processing

   The following tests MUST be performed on returned TRILL BFD Echo
   frames before other processing.  The RBridge Channel document
   requires that the information in the TRILL Header be given to the BFD

   Is the M-bit in the TRILL Header non-zero?  If so, discard the frame.
   (Multi-destination BFD is a work in progress [MultiBFD].)

   The TRILL BFD Echo frame should have gone exactly two hops so test

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   that the TRILL Header hop count as received was 0x3E (i.e., 0x3D if
   it has already been decremented) and if it is any other value discard
   the frame.  The Rbridge Channel Header in the frame MUST have the MH
   bit equal to one and if it is zero, the frame is discarded.

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5. Management and Operations Considerations

   The TRILL BFD parameters on an RBridge are configurable.  The default
   values are the same as in the IP BFD case [RFC5881], except where
   specified in this document such as for Hop Count.

   It is up to the operator of an RBridge campus to configure the rates
   at which TRILL BFD frames are transmitted on a link to avoid
   congestion (e.g., link, I/O, CPU) and false failure detection. See
   also the discussion of congestion in Section 2 of [RFC5881].

   As stated in [RFC5880]:
      It is worth noting that a single BFD session does not consume a
      large amount of bandwidth.  An aggressive session that achieves a
      detection time of 50 milliseconds, by using a transmit interval of
      16.7 milliseconds and a detect multiplier of 3, will generate 60
      packets per second.  The maximum length of each packet on the wire
      is on the order of 100 bytes, for a total of around 48 kilobits
      per second of bandwidth consumption in each direction.

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6. Default Authentication

   Consistent with TRILL's goal of being able to operate with minimum
   configuration, the default for BFD authentication between neighbor
   RBridges is based on the state of IS-IS shared secret authentication
   for Hellos between those RBridges as detaled below. The BFD
   authentication algorithm and methods in this section MUST be
   implemented at an RBridge if TRILL IS-IS authentication and BFD are
   implemented at that RBrdge. If such BFD authentication is configured
   then its configuration is not restricted by the configuration of IS-
   IS security.

   If IS-IS authentication is not in effect between neighbor RBridges
   then, by default, TRILL BFD between those RBridges is also unsecured.

   If such IS-IS authentication is in effect then, unless configured
   otherwise, TRILL BFD Control frames sent between those RBridges MUST
   use BFD Meticulous Keyed SHA1 authentication [RFC5880].  The BFD
   authentication keys between neighbor RBridges by default are derived
   from the IS-IS shared secret authentication keys for Hellos between
   those RBridges as detailed below. However, such BFD authentication
   keys MAY be configured to some other value.

     HMAC-SHA256 ( ( "TRILL BFD Control" | originPortID | originSysID ),
                   IS-IS-shared-key )

   In the above "|" indicates concatenation, HMAC-SHA256 is as described
   in [FIPS180] [RFC6234], "TRILL BFD Control" is the seventeen byte US
   ASCII [ASCII] string indicated that is then concatenated with the
   2-byte Port ID of the originating port and the 6-bytes IS-IS SystemID
   of the originating RBridge, the last two items being in network byte
   order.  The Port and System IDs are included to minimize exposure of
   the same key to improve resistance to cryptanalysis. IS-IS-shared-key
   is secret keying material being used for IS-IS authentication on the

   The use of the above derived key is accomplished by associating the
   above default authentication type and key with the Key ID of the IS-
   IS-shared key used in the derivation and then using that Key ID in
   the Authentication Section of the BFD Control frame OAM protocol
   specific data. Also Auth Type would be 5 and Auth Len would be 28 in
   the Authentication Section. RBridges MAY be configured to use other
   BFD security modes or keying material or configured to use no

   Authentication for TRILL BFD Echo is a local implementation issue as
   BFD Echo frames are authenticated by their sender when returned by by
   a neighbor. However, if TRILL IS-IS and BFD Control are being
   authenticated to a neighbor and BFD Echo is in use, BFD Echo frames
   to be returned by that neighbor should be authenticated and such

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   authentication should use different keying material from other types
   of authentication.  For example, it could use keying material derived
   as follows, where "|" indicates concatenation:

     HMAC-SHA256 ( ( "TRILL BFD Echo" | originPortID | originSysID ),
                   IS-IS-shared-key )

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7. Security Considerations

   BFD over TRILL utilizes the RBridge Channel extension to the TRILL
   protocol and is generally analogous to BFD over IP. As such, the BFD
   authentication faciliity is available to authenticate BFD over TRILL
   packet payloads but no encryption or other security features are
   provided at the BFD over TRILL level. See the following:

      -  [RFC5881] for general BFD security considerations,

      -  [TRILLChannel] for general RBridge Channel security
         considerations, and

      -  [RFC6325] for general TRILL protocol security considerations.

   Section 3.2 above describes seurity concerns with multi-hop BFD
   Control packets and failure to check the TRILL Header M bit in BFD
   Control packets.

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8. IANA Considerations

   IANA is requested to allocate two Rbridge Channel Protocol numbers
   [TRILLChannel] from the range allocated by Standards Actions, as

       Protocol     Number
       --------     ------
       BFD Control   TBD (2 suggested)
       BFD Echo      TBD (3 suggested)

9. Acknowledgements

   The authors would like to specially thank Dave Katz, an author of
   [RFC5880] and [RFC5881], from which some material herein has been

   The following are thanked for their comments and suggestions: Scott
   Bradner, Stewart Bryant, Stephen Farrell, Eric Gray, Brian Haberman,
   Barry Leiba, Erik Nordmark, John Scudder, Robert Sparks, Martin
   Stiemerling, an Sean Turner.

   This documnt was prepared using raw nroff. All macros used were
   defined in the source file.

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Normative References

   [ASCII] - American National Standards Institute (formerly United
         States of America Standards Institute), "USA Code for
         Information Interchange", ANSI X3.4-1968, 1968.  ANSI X3.4-1968
         has been replaced by newer versions with slight modifications,
         but the 1968 version remains definitive for the Internet.

   [FIPS180] - "Secure Hash Standard (SHS)", United States of American,
         National Institute of Science and Technology, Federal
         Information Processing Standard (FIPS) 180-4, March 2012,

   [IS-IS] - International Organization for Standardization,
         "Intermediate system to Intermediate system routeing
         information exchange protocol for use in conjunction with the
         Protocol for providing the Connectionless-mode NetworkService
         (ISO 8473)," ISO/IEC 10589:2002, Second Edition, Nov 2002.

   [RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate
         Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5880] - Katz, D. and D. Ward, "Bidirectional Forwarding Detection
         (BFD)", RFC 5880, June 2010.

   [RFC5881] - Katz, D. and D. Ward, "Bidirectional Forwarding Detection
         (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June 2010.

   [RFC6213] - Hopps, C. and L. Ginsberg, "IS-IS BFD-Enabled TLV", RFC
         6213, April 2011.

   [RFC6325] - Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
         Ghanwani, "Routing Bridges (RBridges): Base Protocol
         Specification", RFC 6325, July 2011.

   [RFC6327] - Eastlake, D., R. Perlman, A. Ghanwani, D. Dutt, V.
         Manral, "RBridges: Adjacency", RFC 6327, July 2011.

   [TRILLChannel] - Eastlake, D., V. Manral, Y. Li, S. Aldrin, D. Ward,
         "RBridges: RBridge Channel Support in TRILL", draft-ietf-trill-
         rbridge-channel, work in progress.

Informative References

   [802.1AX] - IEEE, "IEEE Standard for Local and metropolitan area
         networks / Link Aggregation", 802.1AX-2008, 1 January 2008.

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   [802.1Q] - IEEE 802.1, "IEEE Standard for Local and metropolitan area
         networks - Virtual Bridged Local Area Networks", IEEE Std
         802.1Q-2011, May 2011.

   [MultiBFD] - Katz, D. and D. Ward, "draft-ietf-bfd-multipoint", work
         in progress.

   [RFC5082] - Gill, V., Heasley, J., Meyer, D., Savola, P., and C.
         Pignataro, "The Generalized TTL Security Mechanism (GTSM)", RFC
         5082, October 2007.

   [RFC6234] - Eastlake 3rd, D. and T. Hansen, "US Secure Hash
         Algorithms (SHA and SHA-based HMAC and HKDF)", RFC 6234, May

   [RFC6291] - Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
         D., and S. Mansfield, "Guidelines for the Use of the "OAM"
         Acronym in the IETF", BCP 161, RFC 6291, June 2011.

   [RFC6361] - Carlson, J. and D. Eastlake 3rd, "PPP Transparent
         Interconnection of Lots of Links (TRILL) Protocol Control
         Protocol", RFC 6361, August 2011.

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Recent Changes Record

   [RFC Editor Note: Please delete this section before publication.]

   From -06 to -07:

    1. Replace normative reference to RFC 20 with a refernce to [ASCII].

    2. Update Author Address information.

    3. In the default BFD authentication key derivation, change
       "OriginatorMAC" to the concatenation of the Port ID and the
       System ID.  OriginatorMAC is simpler and shorter but only works
       for Ethernet links. TRILL supports arbitrary technology links
       between RBridges so you need to use the combination of Port ID
       and System ID to get a globally unique quantity. In addition, if
       an IS-IS authentication method is in use the has a Key ID field
       so that multiple shared secret keys may be in place, then by
       default BFD authentication with such a Key ID field should also
       be used with matching Key ID for matching derived key.

    4. Clarify what it means that a single hop BFD control frame in
       support of link connectivity is send at high priority for cases
       other than Ethernet links.

    5. Add reference in Section 5 to Section 2 of [RFC5881] in
       conngection with congestion control.

    6. Add mandatory to implement support for Demand Mode BFD.

    7. Clarify that the BFD authentication algorithm and methods in
       Section 6 MUST be implemented if TRILL IS-IS Authentication and
       BFD are implemented.

    8. Add some small pieces of explanatory and motivational text that
       make no technical changes, as suggested by the Operations
       Directorate review.

    9. Delete comparison between RBridge Channel and MPLS Generic
       Associated Channel.

   10. Update Author Info.

   11. Various editorial changes.

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Authors' Addresses

   Vishwas Manral
   Hewlett Packard Co.
   19111 Pruneridge Ave.
   Cupertino, CA  95089 USA

   Phone: +1-408-447-0000

   Donald Eastlake 3rd
   Huawei R&D USA
   155 Beaver Street
   Milford, MA  01757 USA

   Phone: +1-508-333-2270

   Dave Ward
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95138 USA


   Ayan Banerjee
   Cumulus Networks
   1089 West Evelyn Avenue
   Sunnyvale, CA 94086 USA


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