BFD Working Group Suping Zhai Internet Draft Huawei Techonologies Co., Ltd. Expires: December 2005 draft-suping-bfd-bgp-static-app-01.txt BFD initializtion with BGP and static routes 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. Abstract This document describes the use of the Bidirectional Forwarding Detection protocol with BGP and the static route over IPv4 or IPv6. The main purpose of this draft is to solve the BFD bootstrap problem with BGP and static routes. As to the encapsulation and demultiplexing issues there have been descriptions in BFD single hop draft [BFD-1HOP] and multi-hop draft [BFD-MULI]. With the BFD interaction with BGP graceful restart, the rules described in BFD single hop [BFD-1HOP] with IS-IS and OSPF graceful restart are also applicable to the BFD with BGP graceful restart, and will not iteratein in this draft. Comments on this draft should be directed to rtg-bfd@ietf.org or to author directly. Conventions used in this document 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 [KEYWORDS]. Suping [Page 1] Internet Draft draft-suping-bfd-bgp-static-app-01.txt June, 2005 1 Introduction One very desirable application for BFD [BFD] is to track IPv4 and IPv6 connectivity between directly-connected systems. There are two kinds of directly-connected systems, inter-AS and intra-AS systems. For the BFD application in the intra-AS system there have been single hop draft [BFD-1HOP] and multihop paths draft [BFD-MULTI]. This document is to resolve the BFD initialization in the inter-AS systems, especially BFD application with BGP. With the BFD in static route over IPv4 or IPv6, there need management configuration to bootstrap the BFD session, this document also list some parameters should be configured to startup the BFD session. 2 Use BFD with BGP The Border Gateway Protocol [BGP] is an inter-Autonomous System routing protocol. BGP uses TCP [TCP] as its transport protocol. TCP meets BGP's transport requirements and is present in virtually all commercial routers and hosts. BGP KEEPALIVE messages can be used to detect the path between the BGP peers, but the granularity of failure detection time is minimum two seconds. For the data plane today of Giga bit interface this detection time will cause many traffic to be lost. So the faster detection mechnism is needed in the data plane. BFD can be used to verify the forwarding ability of an BGP router's adjacencies for this purpose. It should be noted that the purpose of using BFD in this context is not to replace the adjacency timeout mechanism, nor is it to demonstrate that the network is fully functional for the use of the routing protocol, but is simply to advise the routing protocol that there are problems forwarding the data protocol for which the BGP session is running. 2.1 Initialization When use BFD with BGP, this document lists two choices to bootstrap BFD session as followings. And which mechanism is used in implementation is out of the scope of this document. 2.1.1 BFD capabilities advertisement in BGP OPEN message In the BGP protocol OPEN message, there is an Optional Parameters field can contain a list of optional parameters, where each parameter is endcode as a triplet. In the document [BGP] Parameter Type 1 has been defined for Authentication Information. And in document [BGP-CAP] there is another definition about Parameter Type 2 for capabilities advertisement. The parameter contains one or more triples , where each triple is encoded as shown below: Suping [Page 2] Internet Draft draft-suping-bfd-bgp-static-app-01.txt June, 2005 +------------------------------+ | Capability Code (1 octet) | +------------------------------+ | Capability Length (1 octet) | +------------------------------+ | Capability Value (variable) | +------------------------------+ Here we use a new Capability code to indicate the BFD capability, the code value is TBD. The Capability Length is 4, and Capability value is the My Discriminator assigned by the BGP speaker and this discriminator will used as the demultiplexing in the following BFD session. If BFD capability advertisement is not presented in the BGP OPEN message, it is not precluded that BFD discriminator initializtion is supported by other means e.g. through static configuration as shown in the 2.1.2 section. Note that it is possible in some failure scenarios for the network to be in a state such that the BGP comes up, but the BFD session cannot be established, and, more particularly, some data cannot be forwarded. For example in some situation TCP traffic can be forwarded but UDP traffic can't forwarded. To avoid this situation, it would be beneficial to not allow the BGP speaker to establish the session with the BGP peer until the BFD session is up. However, this would preclude the operation of the BGP in an environment in which not all systems support BFD. Therefore, if a BFD session is not in Up state (possibly because the remote system does not support BFD), it is OPTIONAL to preclude the establishment of an BGP session with the BGP peer. The choice of whether to do so SHOULD be controlled by means outside the scope of this specification, such as configuration or other mechanisms. protocol. 2.1.2 Configuration manually For the simplicity in the small scale network, it may be configured manually to provide the necessary parameters to start up the BFD session. The first my discriminator for demultiplexing BFD session is needed to configured in the source/end host or router over which the BFD session is to be running. The second if the BFD session is enabled also needed to be configured. Then the system can run BFD if necessary. 3 BFD initialization with static route 3.1 Initialization by configuration manually When use BFD in the situation of static routes, there is no dedicated route protocol can be used to bootstrap BFD session. The simple way to start up BFD session is through the configuration. My Discriminator for demultiplexing BFD session is needed to configured in the source/end host or router over which the BFD Suping [Page 3] Internet Draft draft-suping-bfd-bgp-static-app-01.txt June, 2005 session is to be running. Whether the BFD session enabled on the system is also needed to be configured. Then the system can start BFD session if necessary according to the configuration parameters. 4 BFD Encapsulation and Demultiplexing with BGP and static routes According to the BFD single hop draft [BFD-1HOP] the BFD payload is encoded in the UDP packet. To consist with the [BFD-1HOP] and when in the inter-AS environment and static routes, the BFD is also encoded in UDP packet. BFD using UDP can be simple because no requirment of retransmission, acknowledgement and sequencing. As to the demultiplex, to align with the single-hop draft [BFD-1HOP] and the multi-hop draft [BFD-MULTI], BFD session with one hop BGP or static routes should be demultiplexed based on the interface and in the multi-hop BGP or static routes BFD sessions can be demultiplexed based on source/destination address pairs. 5 Security Considerations As BFD applied in the BGP peer system, it is encouraged to use BFD authentication functions to avoid BFD abuse. Considering BGP itself has the security mechanisms, when use BGP OPEN message to start up the BFD, it's not mandatory to have authentication in BFD session. When use BFD with static routes, it's option to use BFD authentication functions. Normative References [BFD] Katz, D., and Ward, D., "Bidirectional Forwarding Detection", draft-ietf-bfd-base-02.txt, March, 2005 [BFD-1HOP] Katz, D., and Ward, D., "BFD for IPv4 and IPv6 (Single Hop)", draft-ietf-bfd-v4v6-1hop-02.txt, March, 2005 [BFD-MULTI] D. Katz, and D. Ward, "BFD for Multihop Paths", draft -ietf-bfd-multihop-02.txt, March, 2005 [BFD-LSP] Rahul Aggarwal et al, "BFD For MPLS LSPs", draft-ietf -bfd-mpls-01.txt, expired date August 2005 [TCP] Postel, J., "Transmission Control Protocol - DARPA Internet Program Protocol Specification", STD 7, RFC 793, DARPA, September 1981 [BGP] Y. Rekhter, "A Border Gateway Protocol 4 (BGP-4)", RFC1771, March 1995 [BGP-CAP] R. Chandra et al, "Capabilities Advertisement with BGP-4", RFC3992, November 2002 [BGP-RESTART] Srihari R. Sangli et al, draft-ietf-idr-restart-10.txt, expired date December 2004 Suping [Page 4] Internet Draft draft-suping-bfd-bgp-static-app-01.txt June, 2005 Author's Addresses Suping Zhai Huawei Technologies Co., LTD. No. 3 Xinxi Road, Shangdi, HaiDian District, BeiKing City, The P.R.China Email: zhaisuping@huawei.com Full Copyright Statement Copyright (C) The Internet Society (2005). 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 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. Suping [Page 5] Internet Draft draft-suping-bfd-bgp-static-app-01.txt June, 2005