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

Versions: (draft-manral-trill-bfd-encaps)  00 01         Standards Track
          02 03 04 05 06 07 rfc7175                                     
TRILL Working Group                                            V. Manral
INTERNET-DRAFT                                       Hewlett Packard Co.
Intended status: Proposed Standard                           D. Eastlake
                                                          Huawei R&D USA
                                                                 D. Ward
                                                             A. Banerjee
                                                           Cisco Systems
Expires: November 31, 2012                                  June 1, 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 networks, using UDP and ACH
   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
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   and may be updated, replaced, or obsoleted by other documents at any
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   material or to cite them other than as "work in progress."

   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............................................3
      1.1 Terminology............................................3

      2.  BFD over TRILL.........................................5
      2.1 Sessions and Initialization............................5
      2.2 Relationship to IP and MPLS OAM........................6

      3. TRILL BFD Control Protocol..............................7
      3.1 One-Hop TRILL BFD Control..............................7
      3.2 BFD Control Frame Processing...........................7

      4. TRILL BFD Echo Protocol.................................8
      4.1  BFD Echo Frame Processing.............................8

      5. Management and Operations Considerations...............10
      6. Security Considerations................................11
      7. IANA Considerations....................................12
      8. Acknowledgements.......................................12

      9. References.............................................13
      9.1 Normative References..................................13
      9.2 Informative References................................13

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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] 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, short- duration
   detection of failures in the path between forwarding engines.

   This document describes a TRILL encapsulation for BFD packets for
   networks that do not use IP addressing or for ones where it is not

1.1 Terminology

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

      ACH: Associated Channel Header

      BFD: Bi-directional Forwarding Detection

      IP: Internet Protocol

      IS-IS: Intermediate-System to Intermediate-System

      MPLS: Multi Protocol Label Switching

      PPP: Point-to-Point Protocol

      OAM: Operations, Administration, and Maintenance

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   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 neighbor BFD Echo and one-hop and multi-hop BFD
   Control, as specified below, over the Rbridge Channel facility.
   Multi-destination BFD is beyond the scope of this document, although
   there is work in that area [MultiBFD].  The Rbridge Channel facility
   is specified in [TRILLChannel].

   BFD over TRILL support is similar to BFD over IP support [RFC5881]
   except where differences are explicitly mentioned.  When running BFD
   over TRILL both Single Hop as well as in Multi Hop sessions are

   Asynchronous mode is supported, and the demand mode is not supported
   for TRILL.  BFD over TRILL supports the Echo function, however this
   can be used for only 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 Multi Hop
   sessions the Hop count check can be disabled if the MH flag is one.

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

   New Rbridge Channel types for BFD TRILL Control frame and BFD echo
   packet 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 only a single TRILL BFD
   Control session between two RBridges over a given interface visible
   to TRILL.  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.  Link technology

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   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.

   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.

2.2 Relationship to IP and MPLS OAM

   TRILL BFD uses the TRILL Rbridge Channel [TRILLChannel] similar to
   the way that MPLS OAM protocols use the MPLS Generic Associated
   Channel [RFC5586].  However, the RBridges that implement TRILL are
   IS-IS [IS-IS] based routers, not label switched routers; thus TRILL
   BFD is closer to IPv4/IPv6 BFD than to MPLS BFD.

   TRILL BFD optionally includes support of BFD Echo that is not
   specified for MPLS BFD, due to the one way nature of the basic MPLS

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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 7.

   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 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.
   TRILL support of multi-destination BFD Control is beyond the scope of
   this document, although work is being done in the Area [MultiBFD].

   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

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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.  The TRILL OAM
   protocol number for BFD Echo is given in Section 7.

   TRILL BFD Echo frames SHOULD be sent on a link only if the following
   points 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 RECOMMENDED 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.
   TRILL support of multi-destination BFD Echo is beyond the scope of
   this document.

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

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   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.

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6. Security Considerations

   Consistent with TRILL's goal of being able to operate with minimum
   configuration, the default for BFD authentication between neighbor
   RBridges is based on that state of IS-IS shared secret authentication
   for Hello between those RBridges. However, if such BFD authentication
   is configured then its configuration is independent of that for IS-IS

   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 use
   BFD Meticulous Keyed SHA1 authentication [RFC5880] with keying
   material derived as shown below

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

   where HMAC-SHA256 is described in [FIPS180] [RFC6234], "TRILL BFD
   Control" is the seventeen byte US ASCII [RFC20] string indicated that
   is then concatenated with the 6-byte MAC of the originating port in
   network byte order. The MAC is included to minimize exposure of the
   same key to improve resistance to cryptanalysis. IS-IS-key is the
   secret keying material being used for IS-IS authentication on the
   link. This is accomplished by associating the above default
   authentication type and key with Key ID zero and using that Key ID.
   In the Authentication Section of the BFD Control frame OAM protocol
   specific data, Auth Type would be 5, Auth Len would be 28, and Auth
   Key ID is zero. The RBridges MAY be configured to use other BFD
   security modes or keying material or configured to use no security.

   Authentication for TRILL BFD Echo is a local implementation issue as
   BFD Echo frames are authenticated by their sender when received in
   the form of Echo responses. 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 authenticate SHOULD use different keying material from other
   types of authentication.  For example, it could use keying material
   derived as follows:

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

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7. IANA Considerations

   IANA is request 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)

8. Acknowledgements

   The authors would like to thank Dave Katz the author of [RFC5880] and

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

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9. References

9.1 Normative References

   [FIPS180] US National Institute of Science and Technology, "Secure
         Hash Standard (SHS)", FIP PUB 180-4, 2011.

   [RFC20] - Cerf, V., "ASCII format for network interchange", RFC 20,
         October 1969.

   [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.

9.2 Informative References

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

   [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.

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   [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.

   [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.

   [RFC5586] - Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
         Associated Channel", RFC 5586, June 2009.

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

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

   Phone: +1-408-525-8781

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