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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 Cisco Systems 4 Updates: 5884 (if approved) K. Rajaraman 5 Intended status: Standards Track G. Mirsky 6 Expires: September 06, 2015 Ericsson 7 N. Akiya 8 S. Aldrin 9 Huawei Technologies 10 March 05, 2015 12 Clarifications to RFC 5884 13 draft-ietf-bfd-rfc5884-clarifications-01 15 Abstract 17 This document clarifies the procedures for establishing, maintaining 18 and removing multiple, concurrent BFD sessions for a given described in RFC5884. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on September 06, 2015. 38 Copyright Notice 40 Copyright (c) 2015 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Background . . . . . . . . . . . . . . . . . . . . . . . . . 2 56 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 57 2. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 3 58 2.1. Procedures for establishment of multiple BFD sessions . . 3 59 2.2. Procedures for maintenance of multiple BFD sessions . . . 3 60 2.3. Procedures for removing BFD sessions at the egress LSR . 4 61 2.4. Changing discriminators for a BFD session . . . . . . . . 4 62 3. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 4 63 4. Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . 5 64 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 65 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 66 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 67 8. Normative References . . . . . . . . . . . . . . . . . . . . 5 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 6 of [RFC5884] specifies the procedure for bootstrapping BFD 102 sessions using LSP ping. It further states that a BFD session SHOULD 103 be established for each alternate path that is discovered. This 104 requirement has been the source of some ambiguity as the procedures 105 of establishing concurrent, multiple sessions have not been 106 explicitly specified. This ambiguity can also be attributed in part 107 to the text in Section 7 of [RFC5884] forbidding either end to change 108 local discriminator values in BFD control packets after the session 109 reaches the UP state. The following procedures are described to 110 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 discriminator (remote) 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 The remaining procedures of session establishment are as specified 140 in [RFC5884]. 142 2.2. Procedures for maintenance of multiple BFD sessions 143 Both the ingress LSR and egress LSR use the YourDiscriminator of the 144 received BFD packet to demultiplex BFD sessions. 146 2.3. Procedures for removing BFD sessions at the egress LSR 148 [RFC5884] does not specify an explicit procedure for deleting BFD 149 sessions. The procedure for removing a BFD session established by an 150 out-of-band discriminator exchange using the MPLS LSP ping can 151 improve resource management (like memory etc.) especially in 152 scenarios involving thousands or more of such sessions. A few 153 options are possible here: 155 The BFD session MAY be removed in the egress LSR if the BFD 156 session transitions from UP to DOWN. This can be done after the 157 expiry of a configurable timer started after the BFD session state 158 transitions from UP to DOWN at the egress LSR. 160 The BFD session on the egress LSR MAY be removed by the ingress 161 LSR by using the BFD diagnostic code AdminDown(7) as specified in 162 [RFC5880]. When the ingress LSR wants to remove a session without 163 triggering any state change at the egress, it MAY transmit BFD 164 packets indicating the State as Down(1), diagnostic code 165 AdminDown(7) detectMultiplier number of times. Upon receiving 166 such a packet, the egress LSR MAY remove the BFD session, without 167 triggering a change of state. 169 The procedures to be followed at the egress LSR when BFD 170 session(s) remain in the DOWN state for a significant amount of 171 time is a local matter. Such procedures are outside the scope of 172 this document. 174 All BFD sessions established with the FEC MUST be removed 175 automatically if the FEC is removed. 177 2.4. Changing discriminators for a BFD session 179 The discriminators of a BFD session established over an MPLS LSP 180 cannot be changed when it is in UP state. The BFD session could be 181 removed after a graceful transition to AdminDown state using the BFD 182 diagnostic code AdminDown. A new session could be established with a 183 different discriminator. The initiation of the transition from the 184 Up to Down state can be done either by the ingress LSR or the egress 185 LSR. 187 3. Backwards Compatibility 189 The procedures clarified by this document are fully backward 190 compatible with an existing implementation of [RFC5884]. While the 191 capability to bootstrap and maintain multiple BFD sessions may not be 192 present in current implementations, the procedures outlined by this 193 document can be implemented as a software upgrade without affecting 194 existing sessions. In particular, the egress LSR needs to support 195 multiple BFD sessions per before the ingress LSR is 196 upgraded. 198 4. Encapsulation 200 The encapsulation of BFD packets are the same as specified by 201 [RFC5884]. 203 5. Security Considerations 205 This document clarifies the mechanism to bootstrap multiple BFD 206 sessions per . BFD sessions, naturally, use system 207 and network resources. More BFD sessions means more resources will 208 be used. It is highly important to ensure only minimum number of BFD 209 sessions are provisioned per FEC, and bootstrapped BFD sessions are 210 properly deleted when no longer required. Additionally security 211 measures described in [RFC4379] and [RFC5884] are to be followed. 213 6. IANA Considerations 215 This document does not make any requests to IANA. 217 7. Acknowledgements 219 The authors would like to thank Marc Binderberger for performing 220 thorough reviews and providing valuable suggestions. 222 The authors would like to thank Mudigonda Mallik, Rajaguru Veluchamy 223 and Carlos Pignataro of Cisco Systems for their review comments. 225 8. Normative References 227 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 228 Requirement Levels", BCP 14, RFC 2119, March 1997. 230 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 231 Label Switched (MPLS) Data Plane Failures", RFC 4379, 232 February 2006. 234 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 235 (BFD)", RFC 5880, June 2010. 237 [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, 238 "Bidirectional Forwarding Detection (BFD) for MPLS Label 239 Switched Paths (LSPs)", RFC 5884, June 2010. 241 Authors' Addresses 243 Vengada Prasad Govindan 244 Cisco Systems 246 Email: venggovi@cisco.com 248 Kalyani Rajaraman 249 Ericsson 251 Email: kalyani.rajaraman@ericsson.com 253 Gregory Mirsky 254 Ericsson 256 Email: gregory.mirsky@ericsson.com 258 Nobo Akiya 260 Email: nobo.akiya.dev@gmail.com 262 Sam Aldrin 263 Huawei Technologies 265 Email: aldrin.ietf@gmail.com