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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: April 6, 2015 Ericsson 7 N. Akiya 8 Cisco Systems 9 S. Aldrin 10 Huawei Technologies 11 October 3, 2014 13 Clarifications to RFC 5884 14 draft-grmas-bfd-rfc5884-clarifications-00 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 April 6, 2015. 39 Copyright Notice 41 Copyright (c) 2014 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 . . . 3 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 . . . . . . . . . . . . . . . . . . . 4 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 . . . . . . . . . . . . . . . . . . . . . . . 5 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. Since the BFD local discriminator of 128 either ends cannot change as long as the session is in the UP 129 state, a new discriminator received in the LSP ping unambiguously 130 conveys the intent of the LSR ingress to bootstrap a new BFD 131 session for the FEC specified in the LSP ping. 133 Ensure the uniqueness of the tuple. 136 The remaining procedures of session establishment are as specified 137 in [RFC5884]. 139 2.2. Procedures for maintenance of multiple BFD sessions 141 Both the ingress LSR and egress LSR use the YourDiscriminator of the 142 received BFD packet to demultiplex BFD sessions. 144 2.3. Procedures for removing BFD sessions at the egress LSR 146 [RFC5884] does not specify an explicit procedure for deleting BFD 147 sessions. The procedure for removing a BFD session established by an 148 out-of-band discriminator exchange using the MPLS LSP ping can 149 improve resource management (like memory etc.) especially in 150 scenarios involving thousands or more of such sessions. A few 151 options are possible here: 153 The BFD session MAY be removed in the egress LSR if the BFD 154 session transitions from UP to DOWN. This can be done after the 155 expiry of a configurable timer started after the BFD session state 156 transitions from UP to DOWN at the egress LSR. 158 The BFD session on the egress LSR MAY be gracefully removed by the 159 ingress LSR by using the BFD diagnostic code AdminDown(7) 160 specified in [RFC5880]. When the ingress LSR wants to gracefully 161 remove a session, it MAY transmit BFD packets containing the 162 diagnostic code AdminDown(7) detectMultiplier number of times. 163 Upon receiving such a packet, the egress LSR MAY remove the BFD 164 session gracefully, without triggering a change of state. 166 Ed Note: The procedures to be followed at the egress LSR when the BFD 167 session never transitions to UP from DOWN state are yet to be 168 clarified 170 Regardless of the option chosen to proceed, all BFD sessions 171 established with the FEC MUST be removed automatically if the FEC is 172 removed. 174 2.4. Changing discriminators for a BFD session 176 The discriminators of a BFD session established over an MPLS LSP 177 cannot be changed when it is in UP state. The BFD session could be 178 removed after a graceful transition to AdminDown state using the BFD 179 diagnostic code AdminDown. A new session could be established with a 180 different discriminator. The initiation of the transition from the 181 Up to Down state can be done either by the ingress LSR or the egress 182 LSR. 184 3. Backwards Compatibility 186 The procedures clarified by this document are fully backward 187 compatible with an existing implementation of [RFC5884]. While the 188 capability to bootstrap and maintain multiple BFD sessions may not be 189 present in current implementations, the procedures outlined by this 190 document can be implemented as a software upgrade without affecting 191 existing sessions. In particular, the egress LSR needs to support 192 multiple BFD sessions per before the ingress LSR is 193 upgraded. 195 4. Encapsulation 197 The encapsulation of BFD packets are the same as specified by 198 [RFC5884]. 200 5. Security Considerations 202 This document clarifies the mechanism to bootstrap multiple BFD 203 sessions per . BFD sessions, naturally, use system 204 and network resources. More BFD sessions means more resources will 205 be used. It is highly important to ensure only minimum number of BFD 206 sessions are provisioned per FEC, and bootstrapped BFD sessions are 207 properly deleted when no longer required. Additionally security 208 measures described in [RFC4379] and [RFC5884] are to be followed. 210 6. IANA Considerations 212 This document does not make any requests to IANA. 214 7. Acknowledgements 216 The authors would like to thank Mudigonda Mallik, Rajaguru Veluchamy 217 and Carlos Pignataro of Cisco Systems for their review comments. 219 8. Normative References 221 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 222 Requirement Levels", BCP 14, RFC 2119, March 1997. 224 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 225 Label Switched (MPLS) Data Plane Failures", RFC 4379, 226 February 2006. 228 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 229 (BFD)", RFC 5880, June 2010. 231 [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, 232 "Bidirectional Forwarding Detection (BFD) for MPLS Label 233 Switched Paths (LSPs)", RFC 5884, June 2010. 235 Authors' Addresses 236 Vengada Prasad Govindan 237 Cisco Systems 239 Email: venggovi@cisco.com 241 Kalyani Rajaraman 242 Ericsson 244 Email: kalyani.rajaraman@ericsson.com 246 Gregory Mirsky 247 Ericsson 249 Email: gregory.mirsky@ericsson.com 251 Nobo Akiya 252 Cisco Systems 254 Email: nobo@cisco.com 256 Sam Aldrin 257 Huawei Technologies 259 Email: aldrin.ietf@gmail.com