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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: December 18, 2015 Ericsson 7 N. Akiya 8 Big Switch Networks 9 S. Aldrin 10 Google 11 June 16, 2015 13 Clarifications to RFC 5884 14 draft-ietf-bfd-rfc5884-clarifications-02 16 Abstract 18 This document clarifies the procedures for establishing, maintaining 19 and removing multiple, concurrent BFD 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 December 18, 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. 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 . . . . . . . . 4 63 3. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 5 64 4. Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . 5 65 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 66 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 67 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 68 8. Normative References . . . . . . . . . . . . . . . . . . . . 5 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 71 1. Background 73 [RFC5884] defines the procedures to bootstrap and maintain BFD 74 sessions for a using LSP ping. While Section 4 of 75 [RFC5884] specifies that multiple BFD sessions can be established for 76 a tuple, the procedures to bootstrap and maintain 77 multiple BFD sessions concurrently over a are not 78 clearly specified. Additionally, the procedures of removing BFD 79 sessions bootstrapped on the egress LSR are unclear. This document 80 provides those clarifications without deviating from the principles 81 outlined in [RFC5884]. 83 The ability for an ingress LSR to establish multiple BFD sessions for 84 a tuple is useful in scenarios such as Segment 85 Routing based LSPs or LSPs having Equal-Cost Multipath (ECMP). The 86 process used by the ingress LSR to determine the number of BFD 87 session(s) to be bootstrapped for a tuple and the 88 mechanism of constructing those session(s) are outside the scope of 89 this document. 91 1.1. Requirements Language 93 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 94 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 95 "OPTIONAL" in this document are to be interpreted as described in 96 [RFC2119]. 98 2. Theory of Operation 100 2.1. Procedures for establishment of multiple BFD sessions 102 Section 6 of [RFC5884] specifies the procedure for bootstrapping BFD 103 sessions using LSP ping. It further states that a BFD session SHOULD 104 be established for each alternate path that is discovered. This 105 requirement has been the source of some ambiguity as the procedures 106 of establishing concurrent, multiple sessions have not been 107 explicitly specified. This ambiguity can also be attributed in part 108 to the text in Section 7 of [RFC5884] forbidding either end to change 109 local discriminator values in BFD control packets after the session 110 reaches the UP state. The following procedures are described to 111 clarify the ambiguity based on the interpretation of the authors's 112 reading of the referenced sections: 114 At the ingress LSR: 116 MPLS LSP ping can be used to bootstrap multiple BFD sessions for a 117 given . Each LSP ping MUST carry a different 118 discriminator value in the BFD discriminator TLV [RFC4379]. 120 The egress LSR needs to perform the following: 122 If the validation of the FEC in the MPLS Echo request message 123 succeeds, check the discriminator specified in the BFD 124 discriminator TLV of the MPLS Echo request. If there is no local 125 session that corresponds to the discriminator (remote) received in 126 the MPLS Echo request, a new session is bootstrapped and a local 127 discriminator is allocated. The validation of a FEC is a 128 necessary condition to be satisfied to create a new BFD session at 129 the egress LSR. However, the policy or procedure if any, to be 130 applied by the egress LSR before allowing a new BFD session to be 131 created is outside the scope of this document. Such policies or 132 procedures could consider availability of system resources before 133 allowing a session to be created. When the egress LSR disallows 134 the creation of a BFD session due to policy, it MUST drop the MPLS 135 Echo request message. 137 Ensure the uniqueness of the tuple. 140 The remaining procedures of session establishment are as specified 141 in [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 be done after the 159 expiry of a configurable timer started after the BFD session state 160 transitions from UP to DOWN at the egress LSR. 162 The BFD session on the egress LSR MAY be removed by the ingress 163 LSR by using the BFD diagnostic code AdminDown(7) as specified in 164 [RFC5880]. When the ingress LSR wants to remove a session without 165 triggering any state change at the egress, it MAY transmit BFD 166 packets indicating the State as Down(1), diagnostic code 167 AdminDown(7) detectMultiplier number of times. Upon receiving 168 such a packet, the egress LSR MAY remove the BFD session, without 169 triggering a change of state. 171 The procedures to be followed at the egress LSR when BFD 172 session(s) remain in the DOWN state for a significant amount of 173 time is a local matter. Such procedures are outside the scope of 174 this document. 176 All BFD sessions established with the FEC MUST be removed 177 automatically if the FEC is removed. 179 The egress MUST use the discriminators exchanged when the session 180 was brought UP, to indicate any session state change to the 181 ingress. The egress SHOULD reset this to zero after transmitting 182 bfd.detectMult number of packets if the BFD session transitions to 183 DOWN state. 185 2.4. Changing discriminators for a BFD session 187 The discriminators of a BFD session established over an MPLS LSP 188 cannot be changed when it is in UP state. The BFD session could be 189 removed after a graceful transition to AdminDown state using the BFD 190 diagnostic code AdminDown. A new session could be established with a 191 different discriminator. The initiation of the transition from the 192 Up to Down state can be done either by the ingress LSR or the egress 193 LSR. 195 3. Backwards Compatibility 197 The procedures clarified by this document are fully backward 198 compatible with an existing implementation of [RFC5884]. While the 199 capability to bootstrap and maintain multiple BFD sessions may not be 200 present in current implementations, the procedures outlined by this 201 document can be implemented as a software upgrade without affecting 202 existing sessions. In particular, the egress LSR needs to support 203 multiple BFD sessions per before the ingress LSR is 204 upgraded. 206 4. Encapsulation 208 The encapsulation of BFD packets are the same as specified by 209 [RFC5884]. 211 5. Security Considerations 213 This document clarifies the mechanism to bootstrap multiple BFD 214 sessions per . BFD sessions, naturally, use system 215 and network resources. More BFD sessions means more resources will 216 be used. It is highly important to ensure only minimum number of BFD 217 sessions are provisioned per FEC, and bootstrapped BFD sessions are 218 properly deleted when no longer required. Additionally security 219 measures described in [RFC4379] and [RFC5884] are to be followed. 221 6. IANA Considerations 223 This document does not make any requests to IANA. 225 7. Acknowledgements 227 The authors would like to thank Marc Binderberger for performing 228 thorough reviews and providing valuable suggestions. 230 The authors would like to thank Mudigonda Mallik, Rajaguru Veluchamy 231 and Carlos Pignataro of Cisco Systems for their review comments. 233 8. Normative References 235 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 236 Requirement Levels", BCP 14, RFC 2119, March 1997. 238 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 239 Label Switched (MPLS) Data Plane Failures", RFC 4379, 240 February 2006. 242 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 243 (BFD)", RFC 5880, June 2010. 245 [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, 246 "Bidirectional Forwarding Detection (BFD) for MPLS Label 247 Switched Paths (LSPs)", RFC 5884, June 2010. 249 Authors' Addresses 251 Vengada Prasad Govindan 252 Cisco Systems 254 Email: venggovi@cisco.com 256 Kalyani Rajaraman 257 Cisco Systems 259 Email: kalyanir@cisco.com 261 Gregory Mirsky 262 Ericsson 264 Email: gregory.mirsky@ericsson.com 266 Nobo Akiya 267 Big Switch Networks 269 Email: nobo.akiya.dev@gmail.com 271 Sam Aldrin 272 Google 274 Email: aldrin.ietf@gmail.com