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. 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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]