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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-11) exists of draft-ietf-bfd-seamless-base-04 == Outdated reference: A later version (-06) exists of draft-ietf-bfd-seamless-ip-01 == Outdated reference: A later version (-15) exists of draft-ietf-spring-segment-routing-01 Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force N. Akiya 3 Internet-Draft C. Pignataro 4 Intended status: Standards Track N. Kumar 5 Expires: August 27, 2015 Cisco Systems 6 February 23, 2015 8 Seamless Bidirectional Forwarding Detection (S-BFD) for Segment Routing 9 draft-akiya-bfd-seamless-sr-04 11 Abstract 13 This document defines procedures to use Seamless Bidirectional 14 Forwarding Detection (S-BFD) for the Segment Routing environment. 16 Requirements Language 18 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 19 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 20 document are to be interpreted as described in RFC 2119 [RFC2119]. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on August 27, 2015. 39 Copyright Notice 41 Copyright (c) 2015 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 2. Inheritance of Code Points and Procedures . . . . . . . . . . 2 58 3. SBFDInitiator Models . . . . . . . . . . . . . . . . . . . . 3 59 3.1. Uncontrolled Return Path . . . . . . . . . . . . . . . . 3 60 3.2. Controlled Return Path . . . . . . . . . . . . . . . . . 3 61 4. S-BFD Echo Recommendations . . . . . . . . . . . . . . . . . 5 62 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 63 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 64 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 65 8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 6 66 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 67 9.1. Normative References . . . . . . . . . . . . . . . . . . 6 68 9.2. Informative References . . . . . . . . . . . . . . . . . 7 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 71 1. Introduction 73 Seamless Bidirectional Forwarding Detection (S-BFD), 74 [I-D.ietf-bfd-seamless-base], defines a generalized mechanism to 75 allow network nodes to seamlessly perform continuity checks to remote 76 entities. This document defines necessary procedures to use S-BFD on 77 the Segment Routing environment described by 78 [I-D.ietf-spring-segment-routing]. 80 The reader is expected to be familiar with the IP, MPLS, Segment 81 Routing [I-D.ietf-spring-segment-routing], BFD [RFC5880] and S-BFD 82 [I-D.ietf-bfd-seamless-base] terminologies and protocol constructs. 84 2. Inheritance of Code Points and Procedures 86 S-BFD on the Segment Routing MUST use the code points and procedures 87 defined in [I-D.ietf-bfd-seamless-ip] regarding following aspects: 89 o S-BFD Control UDP Port 91 o S-BFD Echo UDP Port 93 o S-BFD Control Packet Demultiplexing 95 o Initiator Procedures 96 o Responder Procedures 98 The Segment Routing on the MPLS data plane is to use MPLS based 99 procedures, and the Segment Routing on the IPv6 data plane is to use 100 IP based procedures. 102 3. SBFDInitiator Models 104 The S-BFD technology defines an SBFDReflector and how SBFDInitiators 105 speak to SBFDReflectors. Outside of these definitions, 106 implementations are free to be flexible in terms of how 107 SBFDInitiators behave. The packet steering capability of the Segment 108 Routing allows for, at very high level, two distinct SBFDInitiator 109 models. This section describes the two SBFDInitiator models as an 110 implementation reference. 112 3.1. Uncontrolled Return Path 114 A network node sending S-BFD control packets to a remote target with 115 particular segment stack will allow the network node to determine 116 whether or not such packets reach the intended remote target. The 117 network node can conclude the reachability when valid response S-BFD 118 control packets are received back. In opposite, the network node can 119 conclude the lack of reachability when valid response S-BFD control 120 packet are not received back. Because S-BFD control packets back 121 from the responder to the initiator will be IP routed, how S-BFD 122 control packets traverse the network back to the initiator is 123 uncontrolled. If the network employs good set of local protection 124 mechanisms, this may not be concerning and the model of only sending 125 S-BFD control packets may be sufficient. 127 In this model, SBFDInitiator is to send only S-BFD control packets. 129 3.2. Controlled Return Path 131 In addition to SBFDInitiator sending S-BFD control packets, described 132 in Section 3.1, S-BFD echo packets can also be sent. 134 +-----B-------C-----+ 135 / \ 136 A-----------E-----------D 137 \ / 138 +-----F-------G-----+ 140 Forward Paths: A-B-C-D 141 IP Return Paths: D-E-A 143 Figure 1: S-BFD Echo Example 145 Node A sending S-BFD control packets with segment stack {B, C, D} 146 will cause S-BFD control packets to traverse the paths A-B-C-D in the 147 forward direction. The response S-BFD control packets from node D 148 back to node A will be IP routed and will traverse the paths D-E-A. 149 The SBFDInitiator sending such packets can also send S-BFD echo 150 packets with segment stack {B, C, D, C, A}. S-BFD echo packets will 151 u-turn on node D and traverse the paths D-C-B-A. If required, the 152 SBFDInitiator can possess multiple types of S-BFD echo packets, with 153 each having varying return paths. In this particular example, the 154 SBFDInitiator can be sending two types of S-BFD echo packets in 155 addition to S-BFD control packets. 157 o S-BFD control packets 159 * Segment stack: {B, C, D} 161 * Return path: D-E-A 163 o S-BFD echo packets #1 165 * Segment stack: {B, C, D, C, A} 167 * Return path: D-C-B-A 169 o S-BFD echo packets #2 171 * Segment stack: {B, C, D, G, A} 173 * Return path: D-G-F-A 175 The SBFDInitiator can correlate the result of each packet type to 176 determine the nature of the failure. One such example of failure 177 correlation is described in the figure below. 179 +---+-----------------------------------------------------------+ 180 | | S-BFD Echo Pkt | 181 | +------------------------------------+----------------------+ 182 | | Success | Failure | 183 +-+-+------------------------------------+----------------------+ 184 | |S| | | 185 |S|u| | | 186 |||c| |Forward SID stack good| 187 |B|c| All is well |Return SID stack bad | 188 |F|e| |Return IP path good | 189 |D|s| | | 190 | |s| | | 191 |C+-+----------------------+-------------+----------------------+ 192 |t|F|Forward SID stack good| | | 193 |r|a|Return SID stack good |Send Alert | | 194 |l|i|Return IP path bad |Discrim S-BFD| | 195 | |l+--------- OR ---------+w/ Forward |Forward SID stack bad | 196 |P|u|Forward SID stack is |SID stack to | | 197 |k|r|terminating on wrong |differentiate| | 198 |t|e|node | | | 199 +-+-+----------------------+-------------+----------------------+ 201 Figure 2: SBFDInitiator Failure Correlation Example 203 4. S-BFD Echo Recommendations 205 o It is RECOMMENDED to compute and use smallest number of segment 206 stack to describe the return path of S-BFD echo packets to prevent 207 the segment stack being too large. How SBFDInitiator determines 208 when to use S-BFD echo packets and how to identify corresponding 209 segment stack for the return paths are outside the scope of this 210 document. 212 o It is RECOMMENDED that SBFDInitiator does not send only S-BFD echo 213 packets. S-BFD echo packets are crafted to traverse the network 214 and to come back to self, thus there is no guarantee that S-BFD 215 echo are u-turning on the intended remote target. On the other 216 hand, S-BFD control packets can verify that segment stack of the 217 forward direction reaches the intended remote target. Therefore, 218 an SBFDInitiator SHOULD send S-BFD control packets when sending 219 S-BFD echo packets. 221 o It is RECOMMENDED that, for Segment Routing on the MPLS data 222 plane, destination IP address of S-BFD echo packets is chosen from 223 the 127/8 range for IPv4 and from the 0:0:0:0:0:FFFF:7F00/104 224 range for IPv6. 226 5. Security Considerations 228 Security considerations for S-BFD are discussed in 229 [I-D.ietf-bfd-seamless-base] and [I-D.ietf-bfd-seamless-ip]. 231 6. IANA Considerations 233 This document does not request any new code points from IANA. 235 7. Acknowledgements 237 Authors would like to thank Marc Binderberger from Cisco Systems for 238 providing valuable comments. 240 8. Contributing Authors 242 Dave Ward 243 Cisco Systems 244 Email: wardd@cisco.com 246 Tarek Saad 247 Cisco Systems 248 Email: tsaad@cisco.com 250 Siva Sivabalan 251 Cisco Systems 252 Email: msiva@cisco.com 254 9. References 256 9.1. Normative References 258 [I-D.ietf-bfd-seamless-base] 259 Akiya, N., Pignataro, C., Ward, D., Bhatia, M., and J. 260 Networks, "Seamless Bidirectional Forwarding Detection 261 (S-BFD)", draft-ietf-bfd-seamless-base-04 (work in 262 progress), January 2015. 264 [I-D.ietf-bfd-seamless-ip] 265 Akiya, N., Pignataro, C., and D. Ward, "Seamless 266 Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6 267 and MPLS", draft-ietf-bfd-seamless-ip-01 (work in 268 progress), January 2015. 270 [I-D.ietf-spring-segment-routing] 271 Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., 272 Litkowski, S., Horneffer, M., Shakir, R., Tantsura, J., 273 and E. Crabbe, "Segment Routing Architecture", draft-ietf- 274 spring-segment-routing-01 (work in progress), February 275 2015. 277 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 278 Requirement Levels", BCP 14, RFC 2119, March 1997. 280 9.2. Informative References 282 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 283 (BFD)", RFC 5880, June 2010. 285 Authors' Addresses 287 Nobo Akiya 288 Cisco Systems 290 Email: nobo@cisco.com 292 Carlos Pignataro 293 Cisco Systems 295 Email: cpignata@cisco.com 297 Nagendra Kumar 298 Cisco Systems 300 Email: naikumar@cisco.com