[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-chopps-isis-bfd-tlv) 00 01 02 03 RFC 6213

IS-IS for IP Internets                                          C. Hopps
Internet-Draft                                               L. Ginsberg
Intended status: Standards Track                           Cisco Systems
Expires: September 11, 2008                               March 10, 2008


                         IS-IS BFD Enabled TLV
                       draft-ietf-isis-bfd-tlv-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 September 11, 2008.

Abstract

   This document describes a TLV for use in the IS-IS routing protocol
   that allows for the proper use of the Bidirectional Forwarding
   Detection protocol (BFD).  There exist certain scenarios in which
   IS-IS will not react appropriately to a BFD detected forwarding plane
   failure without use of either this TLV or some other method.

Requirements Language

   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 [RFC2119].




Hopps & Ginsberg       Expires September 11, 2008               [Page 1]

Internet-Draft            IS-IS BFD Enabled TLV               March 2008


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  The Problem . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  The Solution  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  State Definitions . . . . . . . . . . . . . . . . . . . . . 4
     3.2.  Adjacency Establishment and Maintenance . . . . . . . . . . 4
     3.3.  Advertisement of Topology Specific IS Neighbors . . . . . . 5
   4.  Transition  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Graceful Restart  . . . . . . . . . . . . . . . . . . . . . . . 5
   6.  The BFD Enabled TLV . . . . . . . . . . . . . . . . . . . . . . 6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     10.1. Normative References  . . . . . . . . . . . . . . . . . . . 7
     10.2. Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9
































Hopps & Ginsberg       Expires September 11, 2008               [Page 2]

Internet-Draft            IS-IS BFD Enabled TLV               March 2008


1.  Introduction

   The Bidirectional Forwarding Detection protocol [I-D.ietf-bfd-base]
   is a protocol that allows for detection of a forwarding plane failure
   between two routers.  A router can use [I-D.ietf-bfd-base] to
   validate that a peer router's forwarding ability is functioning.

   One specific application of BFD as described in
   [I-D.ietf-bfd-generic] is to verify the forwarding ability of an
   IS-IS [RFC1195] router's adjacencies; however, the method described
   in [I-D.ietf-bfd-generic] does not allow for certain failure
   scenarios.  We will define a TLV that will allow for proper response
   to the detection of all forwarding failures where the use of BFD is
   employed with IS-IS.


2.  The Problem

   We observe that to allow for mixed use (i.e., some routers running
   BFD and some not) [I-D.ietf-bfd-generic] does not require a BFD
   session be established prior to the establishment of an IS-IS
   adjacency.  Thus, if a router A has neighbors B and C, and B does not
   support BFD, A would still form adjacencies with B and C, and would
   only establish a BFD session with C.

   The problem with this solution is that it assumes that the
   transmission and receipt of IS-IS IIHs shares fate with forwarded
   data packets.  This is not a fair assumption to make given that the
   primary use of BFD is to protect IPv4 (and IPv6) forwarding and IS-IS
   does not utilize IPv4 or IPv6 for sending or receiving its hellos.

   Thus, if we consider our previous example, and if C is currently
   experiencing an IPv4 forwarding failure that allows for IS-IS IIHs to
   be sent and received, when A first starts (or restarts) A will assume
   that C simply does not support BFD, will form an adjacency with C,
   and may incorrectly forward IPv4 traffic through C.


3.  The Solution

   A simple solution to this problem is for an IS-IS router to advertise
   that it has BFD enabled on a given interface.  It can do this through
   the inclusion of a TLV in its IIHs, and indeed that is our proposal.

   When sending an IIH on a BFD enabled interface, a router which
   supports this extension MUST include the BFD enabled TLV in its IIH.
   The contents of the TLV MUST indicate what topologies/protocols
   [RFC5120] have been enabled for BFD by including the appropriate



Hopps & Ginsberg       Expires September 11, 2008               [Page 3]

Internet-Draft            IS-IS BFD Enabled TLV               March 2008


   MTID/NLPID pairs.

   When sending an IIH on an interface on which BFD is NOT enabled a
   router MUST NOT include the BFD enabled TLV.

3.1.  State Definitions

   The following definitions apply to each IS-IS neighbor:

   For each locally supported MTID/NLPID pair, an
   ISIS_TOPO_NLPID_BFD_STATE variable is assigned.  If BFD is supported
   by both the local system and the neighbor, this variable follows the
   BFD session state for that MTID/NLPID (UP == TRUE).  Otherwise the
   variable is set to TRUE.

   For each locally supported MTID/NLPID pair, an
   ISIS_TOPO_NLPID_BFD_REQUIRED variable is assigned.  If BFD is
   supported by both the local system and the neighbor, this variable is
   set to TRUE.  Otherwise the variable is set to FALSE.

   For each locally supported topology (MTID), an
   ISIS_TOPO_USEABLE_STATE variable is set to the logical OR of the set
   of ISIS_TOPO_NLPID_BFD_STATE variables associated with that MTID.

   An ISIS_BFD_UP_STATE variable is set to the logical AND of all
   ISIS_TOPO_NLPID_BFD_STATE variables.

   An ISIS_BFD_REQUIRED variable is set to the logical AND of all
   ISIS_TOPO_NLPID_BFD_REQUIRED variables.

3.2.  Adjacency Establishment and Maintenance

   Whenever ISIS_BFD_REQUIRED is TRUE the following extensions to the
   rules for adjacency establishment and maintenance MUST apply:

   o  ISIS_BFD_UP_STATE MUST be TRUE before the adjacency can transition
      from INIT to UP state

   o  When the IS-IS adjacency is UP and ISIS_BFD_UP_STATE becomes FALSE
      the IS-IS adjacency MUST transition to DOWN.

   o  On a Point-to-Point circuit whenever ISIS_BFD_UP_STATE is FALSE,
      the Three-Way adjacency state MUST be set to DOWN in the Point-to-
      Point Three Way Adjacency TLV[RFC3373] in all transmitted IIHs.

   o  On a LAN circuit whenever ISIS_BFD_UP_STATE is FALSE, the IS
      Neighbors TLV advertising the MAC address of the neighbor MUST be
      omitted in all transmitted IIHs.



Hopps & Ginsberg       Expires September 11, 2008               [Page 4]

Internet-Draft            IS-IS BFD Enabled TLV               March 2008


3.3.  Advertisement of Topology Specific IS Neighbors

   The advertisement of a topology specific IS-neighbor (as well as the
   use of the neighbor in the topology specific decision process) is
   determined by the value of ISIS_TOPO_USEABLE_STATE for each topology.
   If ISIS_TOPO_USEABLE_STATE is TRUE then the topology specific
   neighbor is advertised.  If ISIS_TOPO_USEABLE_STATE is FALSE then the
   topology specific neighbor is NOT advertised.


4.  Transition

   To allow for a non-disruptive transition to the use of BFD some
   amount of time should be allowed before bringing down an UP adjacency
   on a BFD enabled interface when the value of ISIS_BFD_REQUIRED
   becomes TRUE as a result of the introduction of the BFD TLV or the
   modification (by adding a new supported MTID/NLPID) of an existing
   BFD TLV in a neighbor's IIH.  A simple way to do this is to not
   update the adjacency hold-time when receiving such an IIH from a
   neighbor with whom we have an UP adjacency until ISIS_BFD_UP_STATE
   becomes TRUE.

   If the value of ISIS_BFD_REQUIRED becomes FALSE as a result of the
   removal the BFD TLV or the modification (by removing a supported
   MTID/NLPID) of an existing BFD TLV in a neighbor's IIH then BFD
   session establishment is no longer required to maintain the adjacency
   or transition the adjacency to the UP state.

   If a BFD session is administratively shut down [I-D.ietf-bfd-base]
   and the BFD session state change impacts the value of
   ISIS_BFD_UP_STATE, then IS-IS SHOULD allow time for the corresponding
   MTID/NLPID to be removed from the neighbor's BFD TLV by not updating
   the adjacency hold time until ISIS_BFD_REQUIRED becomes FALSE.  Note
   that while this allows a non-disruptive transition, it still enforces
   consistency between the administrative state of the BFD session and
   the MTID/NLPID(s) advertised in the BFD TLV.  This is necessary to
   provide consistent behavior regardless of whether the BFD AdminDown
   state is introduced before or after an IS-IS adjacency UP state has
   been achieved.


5.  Graceful Restart

   It is worth considering what if anything should be done when IS-IS is
   gracefully restarting [RFC3847].

   In cases where BFD shares fate with the control plane, it can be
   expected that BFD session failure may occur in conjunction with the



Hopps & Ginsberg       Expires September 11, 2008               [Page 5]

Internet-Draft            IS-IS BFD Enabled TLV               March 2008


   control plane restart.  In such cases premature abort of IS-IS
   graceful restart as a result of BFD session failure is undesirable.
   Therefore, some mechanism to ignore the BFD session failure for a
   limited period of time would be beneficial.  How this is implemented
   is beyond the scope of this document.  Consult [I-D.ietf-bfd-generic]
   for further details.


6.  The BFD Enabled TLV

   The BFD enabled TLV is formatted as shown below.  The TLV SHALL only
   be included in an IS-IS IIH PDU and only when BFD is enabled for one
   or more supported MTID/protocols on the interface over which the IIH
   is being sent.  The NLPIDs encoded in the TLV are defined in
   [ISO9577]

     Type   139 (suggested - to be assigned by IANA)
     Length # of octets in the value field (3 to 255)
     Value  three octets specifying the MTID/NLPID for each
            topology/data protocol for which BFD support is enabled

                                          No. of octets
                +-----------------------+
                |R|R|R|R|   MTID        |     2
                +-----------------------+
                |      NLPID            |     1
                +-----------------------+
                :                       :
                :                       :
                +-----------------------+
                |R|R|R|R|   MTID        |     2
                +-----------------------+
                | NLPID                 |     1
                +-----------------------+


7.  Security Considerations

   The TLV defined within this document describes an addition to the
   IS-IS Hello protocol and does not impact the security mechanism of
   the IS-IS protocol.


8.  IANA Considerations

   The following IS-IS TLV type is defined by this draft.





Hopps & Ginsberg       Expires September 11, 2008               [Page 6]

Internet-Draft            IS-IS BFD Enabled TLV               March 2008


   Name                                  Value  IIH   LSP  SNP
   ----------------------                -----  ---   ---  ---
   BFD Enabled TLV                         139   y     n    n

   Please update the IS-IS TLV Codepoint Registry accordingly.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.


9.  Acknowledgements

   The authors wish to thank Matthew Jones, Dave Katz, Jonathan Moon,
   Stefano Previdi, Michael Shiplett and David Ward, for various input
   on this document.


10.  References

10.1.  Normative References

   [ISO9577]  International Organization for Standardization, "Protocol
              identification in the network layer(ISO/IEC 9577)", ISO/
              IEC 9577:1999, Fourth Edition, Dec 1999.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, December 1990.

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

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120, February 2008.

10.2.  Informative References

   [I-D.ietf-bfd-base]
              Katz, D. and D. Ward, "Bidirectional Forwarding
              Detection", draft-ietf-bfd-base-07 (work in progress),
              January 2008.

   [I-D.ietf-bfd-generic]
              Katz, D. and D. Ward, "Generic Application of BFD",
              draft-ietf-bfd-generic-04 (work in progress),
              January 2008.

   [RFC3373]  Katz, D. and R. Saluja, "Three-Way Handshake for



Hopps & Ginsberg       Expires September 11, 2008               [Page 7]

Internet-Draft            IS-IS BFD Enabled TLV               March 2008


              Intermediate System to Intermediate System (IS-IS) Point-
              to-Point Adjacencies", RFC 3373, September 2002.

   [RFC3847]  Shand, M. and L. Ginsberg, "Restart Signaling for
              Intermediate System to Intermediate System (IS-IS)",
              RFC 3847, July 2004.


Authors' Addresses

   Christian E. Hopps
   Cisco Systems
   170 W. Tasman Dr.
   San Jose, California  95134
   USA

   Email: chopps@cisco.com


   Les Ginsberg
   Cisco Systems
   510 McCarthy Blvd.
   Milpitas, Ca.  95035
   USA

   Email: ginsberg@cisco.com

























Hopps & Ginsberg       Expires September 11, 2008               [Page 8]

Internet-Draft            IS-IS BFD Enabled TLV               March 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.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.











Hopps & Ginsberg       Expires September 11, 2008               [Page 9]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/