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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) ** Obsolete normative reference: RFC 4379 (Obsoleted by RFC 8029) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force V. Govindan 3 Internet-Draft K. Rajaraman 4 Updates: 5884 (if approved) Cisco Systems 5 Intended status: Standards Track G. Mirsky 6 Expires: April 16, 2016 Ericsson 7 N. Akiya 8 Big Switch Networks 9 S. Aldrin 10 Google 11 October 14, 2015 13 Clarifications to RFC 5884 14 draft-ietf-bfd-rfc5884-clarifications-04 16 Abstract 18 This document clarifies the procedures for establishing, maintaining 19 and removing multiple, concurrent BFD (Bidirectional Forwarding 20 Detection) sessions for a given described in RFC5884. 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 April 16, 2016. 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. Background . . . . . . . . . . . . . . . . . . . . . . . . . 2 57 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 58 2. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 3 59 2.1. Procedures for establishment of multiple BFD sessions . . 3 60 2.2. Procedures for maintenance of multiple BFD sessions . . . 4 61 2.3. Procedures for removing BFD sessions at the egress LSR . 4 62 2.4. Changing discriminators for a BFD session . . . . . . . . 5 63 3. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 5 64 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5 65 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 66 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 67 7. Normative References . . . . . . . . . . . . . . . . . . . . 6 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 70 1. Background 72 [RFC5884] defines the procedures to bootstrap and maintain BFD 73 sessions for a using LSP ping. While Section 4 of 74 [RFC5884] specifies that multiple BFD sessions can be established for 75 a tuple, the procedures to bootstrap and maintain 76 multiple BFD sessions concurrently over a are not 77 clearly specified. Additionally, the procedures of removing BFD 78 sessions bootstrapped on the egress LSR are unclear. This document 79 provides those clarifications without deviating from the principles 80 outlined in [RFC5884]. 82 The ability for an ingress LSR to establish multiple BFD sessions for 83 a tuple is useful in scenarios such as Segment 84 Routing based LSPs or LSPs having Equal-Cost Multipath (ECMP). The 85 process used by the ingress LSR to determine the number of BFD 86 session(s) to be bootstrapped for a tuple and the 87 mechanism of constructing those session(s) are outside the scope of 88 this document. 90 1.1. Requirements Language 92 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 93 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 94 "OPTIONAL" in this document are to be interpreted as described in 95 [RFC2119]. 97 2. Theory of Operation 99 2.1. Procedures for establishment of multiple BFD sessions 101 Section 4 of [RFC5884] specifies the procedure for bootstrapping BFD 102 sessions using LSP ping. It further states that "a BFD session 103 SHOULD be established for each alternate path that is discovered". 104 This requirement has been the source of some ambiguity as the 105 procedures of establishing concurrent, multiple sessions have not 106 been explicitly specified. This ambiguity can also be attributed in 107 part to the text in Section 7 of [RFC5884] forbidding either end to 108 change local discriminator values in BFD control packets after the 109 session reaches the UP state. The following procedures are described 110 to clarify the ambiguity based on the interpretation of the authors's 111 reading of the referenced sections: 113 At the ingress LSR: 115 MPLS LSP ping can be used to bootstrap multiple BFD sessions for a 116 given . Each LSP ping MUST carry a different 117 discriminator value in the BFD discriminator TLV [RFC4379]. 119 The egress LSR needs to perform the following: 121 If the validation of the FEC in the MPLS Echo request message 122 succeeds, check the discriminator specified in the BFD 123 discriminator TLV of the MPLS Echo request. If there is no local 124 session that corresponds to the (remote) discriminator received in 125 the MPLS Echo request, a new session is bootstrapped and a local 126 discriminator is allocated. The validation of a FEC is a 127 necessary condition to be satisfied to create a new BFD session at 128 the egress LSR. However, the policy or procedure if any, to be 129 applied by the egress LSR before allowing a new BFD session to be 130 created is outside the scope of this document. Such policies or 131 procedures could consider availability of system resources before 132 allowing a session to be created. When the egress LSR disallows 133 the creation of a BFD session due to policy, it MUST drop the MPLS 134 Echo request message. 136 Ensure the uniqueness of the tuple. 139 Except for the clarification mentioned above, the remaining 140 procedures ofBFD session establishment are as specified in 141 Sections 4-6 of [RFC5884]. 143 2.2. Procedures for maintenance of multiple BFD sessions 145 Both the ingress LSR and egress LSR use the YourDiscriminator of the 146 received BFD packet to demultiplex BFD sessions. 148 2.3. Procedures for removing BFD sessions at the egress LSR 150 [RFC5884] does not specify an explicit procedure for deleting BFD 151 sessions. The procedure for removing a BFD session established by an 152 out-of-band discriminator exchange using the MPLS LSP ping can 153 improve resource management (like memory etc.) especially in 154 scenarios involving thousands or more of such sessions. A few 155 observations are made here: 157 The BFD session MAY be removed in the egress LSR if the BFD 158 session transitions from UP to DOWN. This can either be done 159 immediately after the BFD session transitions from UP to DOWN or 160 after the expiry of a configurable timer started after the BFD 161 session state transitions from UP to DOWN at the egress LSR to 162 reduce flapping by adding hysteresis. 164 The BFD session on the egress LSR MAY be removed by the ingress 165 LSR by using the BFD diagnostic code AdminDown(7) as specified in 166 [RFC5880]. When the ingress LSR wants to remove a session without 167 triggering any state change at the egress, it MAY transmit BFD 168 packets indicating the State as Down(1), diagnostic code 169 AdminDown(7) detectMultiplier number of times. Upon receiving 170 such a packet, the egress LSR MAY remove the BFD session, without 171 triggering a change of state. 173 The procedures to be followed at the egress LSR when BFD 174 session(s) remain in the DOWN state for a significant amount of 175 time is a local matter. Such procedures are outside the scope of 176 this document. 178 All BFD sessions established with the FEC MUST be removed 179 automatically if the FEC is removed. 181 The egress MUST use the discriminators exchanged when the session 182 was brought UP, to indicate any session state change to the 183 ingress. The egress SHOULD reset this to zero after transmitting 184 bfd.detectMult number of packets if the BFD session transitions to 185 DOWN state. 187 2.4. Changing discriminators for a BFD session 189 The discriminators of a BFD session established over an MPLS LSP 190 cannot be changed when it is in UP state. The BFD session could be 191 removed after a graceful transition to AdminDown state using the BFD 192 diagnostic code AdminDown. A new session could be established with a 193 different discriminator. The initiation of the transition from the 194 Up to Down state can be done either by the ingress LSR or the egress 195 LSR. 197 3. Backwards Compatibility 199 The procedures clarified by this document are fully backward 200 compatible with an existing implementation of [RFC5884]. While the 201 capability to bootstrap and maintain multiple BFD sessions may not be 202 present in current implementations, the procedures outlined by this 203 document can be implemented as a software upgrade without affecting 204 existing sessions. In particular, the egress LSR needs to support 205 multiple BFD sessions per before the ingress LSR is 206 upgraded. 208 4. Security Considerations 210 This document clarifies the mechanism to bootstrap multiple BFD 211 sessions per . BFD sessions, naturally, use system 212 and network resources. More BFD sessions means more resources will 213 be used. It is highly important to ensure only minimum number of BFD 214 sessions are provisioned per FEC, and bootstrapped BFD sessions are 215 properly deleted when no longer required. Additionally security 216 measures described in [RFC4379] and [RFC5884] are to be followed. 218 5. IANA Considerations 220 This document does not make any requests to IANA. 222 6. Acknowledgements 224 The authors would like to thank Marc Binderberger for performing 225 thorough reviews and providing valuable suggestions. 227 The authors would like to thank Mudigonda Mallik, Rajaguru Veluchamy 228 and Carlos Pignataro of Cisco Systems for their review comments. 230 The authors would like to thank Alvaro Retana and Scott Bradner for 231 their review comments. 233 7. Normative References 235 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 236 Requirement Levels", BCP 14, RFC 2119, 237 DOI 10.17487/RFC2119, March 1997, 238 . 240 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 241 Label Switched (MPLS) Data Plane Failures", RFC 4379, 242 DOI 10.17487/RFC4379, February 2006, 243 . 245 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 246 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 247 . 249 [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, 250 "Bidirectional Forwarding Detection (BFD) for MPLS Label 251 Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884, 252 June 2010, . 254 Authors' Addresses 256 Vengada Prasad Govindan 257 Cisco Systems 259 Email: venggovi@cisco.com 261 Kalyani Rajaraman 262 Cisco Systems 264 Email: kalyanir@cisco.com 266 Gregory Mirsky 267 Ericsson 269 Email: gregory.mirsky@ericsson.com 271 Nobo Akiya 272 Big Switch Networks 274 Email: nobo.akiya.dev@gmail.com 275 Sam Aldrin 276 Google 278 Email: aldrin.ietf@gmail.com