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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group D. Katz 3 Internet Draft Juniper Networks 4 D. Ward 5 Cisco Systems 6 Expires: January, 2006 July, 2005 8 Generic Application of BFD 9 draft-ietf-bfd-generic-00.txt 11 Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that other 20 groups may also distribute working documents as Internet-Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/1id-abstracts.html 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html 33 Copyright Notice 35 Copyright (C) The Internet Society (2005). All Rights Reserved. 37 Abstract 39 This document describes the generic application of the Bidirectional 40 Forwarding Detection (BFD) protocol in environments not specifically 41 documented in other specifications. Comments on this draft should be 42 directed to rtg-bfd@ietf.org. 44 Conventions used in this document 46 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 47 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 48 document are to be interpreted as described in RFC-2119 [KEYWORDS]. 50 1. Introduction 52 BFD [BFD] provides a liveness detection mechanism that can be 53 utilized by other network components for which their integral 54 liveness mechanisms are either too slow, inappropriate, or 55 nonexistent. Other drafts have detailed the use of BFD in specific 56 situations ([BFD-1HOP], [BFD-MULTI], [BFD-MPLS]). As the utility of 57 BFD has become understood, there have been calls to specify BFD 58 interactions with a growing list of network functions. Rather than 59 producing a long series of short documents on the application of BFD, 60 it seemed worthwhile to describe the interactions between BFD and 61 other network functions in a broad way. 63 This document describes the generic application of BFD. Applications 64 with specific requirements should be spelled out in specific 65 documents. 67 2. Overview 69 The Bidirectional Forwarding Detection (BFD) specification defines a 70 protocol with simple and specific semantics. Its sole purpose is to 71 verify connectivity between a pair of systems, for a particular data 72 protocol across a path (which may be of any technology, length, or 73 OSI layer). The promptness of the detection of a path failure can be 74 controlled by trading off protocol overhead and system load with 75 detection times. 77 BFD is *not* intended to directly provide control protocol liveness 78 information; those protocols have their own means and vagaries. 80 Rather, control protocols can use the services provided by BFD to 81 inform their operation. BFD can be viewed as a service provided by 82 the layer in which it is running. 84 The service interface with BFD is straightforward. The application 85 supplies session parameters (neighbor address, time parameters, 86 protocol options), and BFD provides the session state, of which the 87 most interesting transitions are to and from the Up state. The 88 application is expected to bootstrap the BFD session, as BFD has no 89 discovery mechanism. 91 An implementation SHOULD establish only a single BFD session per data 92 protocol path, regardless of the number of applications that wish to 93 utilize it. There is no additional value in having multiple BFD 94 sessions to the same endpoints. If multiple applications request 95 different session parameters, it is a local issue as to how to 96 resolve the parameter conflicts. BFD in turn will notify all 97 applications bound to a session when a session state change occurs. 99 BFD should be viewed as having an advisory role to the protocol or 100 protocols or other network function with which it is interacting, 101 which will then use their own mechanisms to effect any state 102 transitions. The interaction is very much at arm's length, which 103 keeps things simple and decoupled. In particular, BFD explicitly 104 does not carry application-specific information, partly for 105 architectural reasons, and partly because BFD may have curious and 106 unpredictable latency characteristics and as such makes a poor 107 transport mechanism. 109 3. Control Protocol Interactions 111 The object when BFD interacts with a control protocol is to advise 112 the control protocol of the connectivity of the data protocol. In 113 the case of routing protocols, for example, this allows the 114 connectivity failure to trigger the rerouting of traffic around the 115 failed path. 117 The mechanism by which the control protocol achieves its reaction to 118 the path failure depends on the capabilities of the protocol. A 119 protocol which is tightly bound to the failing data protocol may wish 120 to emulate a control protocol failure across the path (such as 121 tearing down an adjacency or peer in a routing protocol that supports 122 only the failed data protocol.) Note that this should not be 123 interpreted as BFD replacing the control protocol liveness mechanism, 124 if any, as the control protocol may rely on mechanisms not verified 125 by BFD (multicast, for instance) so BFD most likely cannot detect all 126 failures that would impact the control protocol. However, a control 127 protocol may choose to use BFD session state information to more 128 rapidly detect an impending control protocol failure, particularly if 129 the control protocol operates in band (over the data protocol.) 131 If the control protocol has a more explicit mechanism for announcing 132 path state, it is preferable to use that mechanism rather than 133 impacting the connectivity of the control protocol (since the control 134 protocol may be supporting other data protocols that are still 135 functioning), particularly if the control protocol operates out of 136 band from the failed data protocol. 138 4. Interactions With Non-Protocol Functions 140 BFD session status may be used to affect other system functions that 141 are not protocol-based (for example, static routes.) If the path to 142 a remote system fails, it may be desirable to not attempt to pass 143 traffic to that remote system, so the local system may wish to take 144 internal measures to accomplish this. Bootstrapping of the BFD 145 session is likely to be derived from configuration information in 146 this case. 148 There is no need to exchange endpoints or discriminator values via 149 any other mechanism than configuration (via OSS or any other means) 150 as the endpoints must be known and configured by the same means. 152 5. Other Application Issues 154 BFD can provide liveness detection for OAM-like functions in 155 tunneling and pseudowire protocols. Running BFD inside the tunnel is 156 recommended, as it exercises more aspects of the path. One way to 157 accommodate this is to address BFD packets based on the tunnel 158 endpoints, assuming that they are numbered. 160 If a planned outage is to take place on a path over which BFD is run, 161 it is preferable to take down the BFD session by going into ADMIN 162 DOWN state prior to the outage. 164 6. Interoperability Issues 166 The BFD protocol itself is designed so that it will always 167 interoperate at a basic level; asynchronous mode is mandatory and is 168 always available, and other modes and functions are negotiated at run 169 time. Since the service provided by BFD is identical regardless of 170 the variants used, the particular choice of BFD options has no 171 bearing on interoperability. 173 The interaction between BFD and other protocols and control functions 174 is very loosely coupled. The actions taken are based on existing 175 mechanisms in those protocols and functions, so interoperability 176 problems are very unlikely unless BFD is applied in contradictory 177 ways (such as a BFD session failure causing one implementation to go 178 down and another implementation to come up.) 180 Normative References 182 [BFD] Katz, D., and Ward, D., "Bidirectional Forwarding Detection", 183 draft-ietf-bfd-base-03.txt, July, 2005. 185 [BFD-1HOP] Katz, D., and Ward, D., "BFD for IPv4 and IPv6 (Single 186 Hop)", draft-ietf-bfd-v4v6-1hop-03.txt, July, 2005. 188 [BFD-MPLS] Aggarwal, R., and Kompella, K., "BFD for MPLS LSPs", 189 draft-ietf-bfd-mpls-01.txt, February, 2005. 191 [BFD-MULTI] Katz, D., and Ward, D., "BFD for Multihop Paths", draft- 192 ietf-bfd-multihop-03.txt, July, 2005. 194 [KEYWORD] Bradner, S., "Key words for use in RFCs to Indicate 195 Requirement Levels", RFC 2119, March 1997. 197 Security Considerations 199 This specification does not raise any additional security issues 200 beyond those of the specifications referred to in the list of 201 normative references. 203 IANA Considerations 205 This document has no actions for IANA. 207 Authors' Addresses 209 Dave Katz 210 Juniper Networks 211 1194 N. Mathilda Ave. 212 Sunnyvale, California 94089-1206 USA 213 Phone: +1-408-745-2000 214 Email: dkatz@juniper.net 216 Dave Ward 217 Cisco Systems 218 170 W. Tasman Dr. 219 San Jose, CA 95134 USA 220 Phone: +1-408-526-4000 221 Email: dward@cisco.com 223 IPR Disclaimer 225 The IETF takes no position regarding the validity or scope of any 226 Intellectual Property Rights or other rights that might be claimed to 227 pertain to the implementation or use of the technology described in 228 this document or the extent to which any license under such rights 229 might or might not be available; nor does it represent that it has 230 made any independent effort to identify any such rights. 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Please address the information to the IETF at ietf- 245 ipr@ietf.org. 247 Full Copyright Notice 249 Copyright (C) The Internet Society (2005). 251 This document is subject to the rights, licenses and restrictions 252 contained in BCP 78, and except as set forth therein, the authors 253 retain all their rights. 255 This document and the information contained herein are provided on an 256 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 257 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 258 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 259 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 260 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 261 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 263 Acknowledgement 265 Funding for the RFC Editor function is currently provided by the 266 Internet Society. 268 This document expires in January, 2006.