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Pignataro 4 Intended status: Standards Track Cisco 5 Expires: October 17, 2016 April 15, 2016 7 Advertising Seamless Bidirectional Forwarding Detection (S-BFD) 8 Discriminators in Layer Two Tunneling Protocol, Version 3 (L2TPv3) 9 draft-ietf-l2tpext-sbfd-discriminator-05 11 Abstract 13 This document defines a new Attribute Value Pair (AVP) that allows 14 L2TP Control Connection Endpoints (LCCEs) to advertise one or more 15 Seamless Bidirectional Forwarding Detection (S-BFD) Discriminator 16 values using the Layer Two Tunneling Protocol, Version 3 (L2TPv3). 18 Requirements Language 20 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 21 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 22 document are to be interpreted as described in RFC 2119 [RFC2119]. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on October 17, 2016. 41 Copyright Notice 43 Copyright (c) 2016 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 59 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. S-BFD Target Discriminator ID AVP . . . . . . . . . . . . . . 2 61 2.1. Encoding Format . . . . . . . . . . . . . . . . . . . . . 3 62 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 63 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 64 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 65 6. Contributing Authors . . . . . . . . . . . . . . . . . . . . 5 66 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 67 7.1. Normative References . . . . . . . . . . . . . . . . . . 5 68 7.2. Informative References . . . . . . . . . . . . . . . . . 5 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 71 1. Introduction 73 [I-D.ietf-bfd-seamless-base] defines a simplified mechanism to use 74 Bidirectional Forwarding Detection (BFD) [RFC5880], referred to as 75 Seamless Bidirectional Forwarding Detection (S-BFD). The S-BFD 76 mechanisms depend on network nodes knowing the BFD discriminators 77 which each node in the network has reserved for this purpose. S-BFD 78 requires the usage of unique discriminators within an administrative 79 domain. The use of Layer Two Tunneling Protocol, Version 3 (L2TPv3) 80 [RFC3931] is one possible means of advertising these discriminators. 82 This document specifies the encoding to be used when S-BFD 83 discriminators are advertised using L2TPv3. 85 1.1. Terminology 87 The reader is expected to be very familiar with the terminology and 88 protocol constructs defined in S-BFD (see Section 2 of 89 [I-D.ietf-bfd-seamless-base]) and L2TPv3 (see Section 1.3 of 90 [RFC3931]). 92 2. S-BFD Target Discriminator ID AVP 94 The "S-BFD Target Discriminator ID" AVP is exchanged using the ICRQ 95 (Incoming-Call-Request), ICRP (Incoming-Call-Reply), OCRQ (Outgoing- 96 Call-Request), and OCRP (Outgoing-Call-Reply) control messages during 97 session negotiations. 99 2.1. Encoding Format 101 The S-BFD Target Discriminator Identifier (ID) Attribute Value Pair 102 (AVP), Attribute Type "TBA by IANA", is an identifier used to 103 advertise the S-BFD Target Discriminator(s) supported by an LCCE for 104 the S-BFD Reflector operation. This AVP indicates that the 105 advertiser implements an S-BFD reflector supporting the specified 106 target discriminator(s) and is ready for S-BFD Reflector operation. 107 The receiving LCCE MAY use this AVP if it wants to monitor 108 connectivity to the advertising LCCE using S-BFD. 110 The Attribute Value field for this AVP has the following format: 112 S-BFD Target Discriminator ID (ICRQ, ICRP, OCRQ, OCRP): 114 No. of octets 115 +-----------------------------+ 116 | Discriminator Value(s) | 4/Discriminator 117 : : 118 +-----------------------------+ 120 An LCCE MAY include the S-BFD Discriminator Advertisement AVP in a 121 L2TP Control Protocol message (ICRQ, ICRP, OCRQ, OCRP) [RFC3931]. If 122 the other LCCE does not wish to monitor connectivity using S-BFD, it 123 MAY safely discard this AVP without affecting the rest of session 124 negotiation. While [I-D.ietf-bfd-seamless-base] concerns itself with 125 the advertisement of only one discriminator unless the mapping to 126 discriminators to entities is specified, the AVP encoding allows the 127 specification of an arbitrary number of S-BFD Discriminators (at 128 least one) for extensibility. 130 When an LCCE uses the S-BFD Target Discriminator ID AVP, multiple 131 S-BFD Discriminators MAY be included, and at least one S-BFD 132 Discriminator MUST be included. When one S-BFD Discriminator is 133 advertised, such S-BFD Discriminator is associated with the L2TPv3 134 Session. When multiple S-BFD discriminators are advertised how a 135 given discriminator is mapped to a specific use case is out of scope 136 for this document. 138 The S-BFD Target Discriminator ID AVP allows for advertising at least 139 one S-BFD Discriminator value: 141 0 1 2 3 142 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 144 | Discriminator 1 | 145 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 146 | Discriminator 2 (Optional) | 147 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 148 | ... | 149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 150 | Discriminator n (Optional) | 151 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 153 The M bit of the L2TP Control Protocol Message (ICRQ, ICRP, OCRQ, 154 OCRP) [RFC3931] MUST NOT be set inside the S-BFD Target Discriminator 155 ID AVP advertisement. 157 3. IANA Considerations 159 IANA maintains a sub-registry "Message Type AVP (Attribute Type 0) 160 Values" in the "Control Message Attribute Value Pairs" as per 161 [RFC3438]. IANA is requested to assign the first free value from 162 this sub-registry as the Message typ AVP for "S-BFD Target 163 Discriminator ID". 165 A summary of the new AVPs requested for Attribute Type 0 follows: 167 Control Message Attribute Value Pairs 169 Attribute 170 Type Description 171 ----------- ------------------ 172 TBA by IANA S-BFD Target Discriminator ID 174 4. Security Considerations 176 Security concerns for L2TP are addressed in [RFC3931]. Introduction 177 of the S-BFD Discriminator Advertisement AVP introduces no new 178 security risks for L2TP. 180 Advertisement of the S-BFD discriminators does make it possible for 181 attackers to initiate S-BFD sessions using the advertised 182 information. The vulnerabilities this poses and how to mitigate them 183 are discussed in the Security Considerations section of 184 [I-D.ietf-bfd-seamless-base]. 186 5. Acknowledgements 188 Authors would like to thank Nobo Akiya, Stewart Bryant and Pawel 189 Sowinski for providing core inputs for the document and for 190 performing thorough reviews and providing number of comments. 191 Authors would like to thank Nagendra Kumar for his reviews. 193 6. Contributing Authors 195 Mallik Mudigonda 196 Cisco Systems, Inc. 198 Email: mmudigon@cisco.com 200 7. References 202 7.1. Normative References 204 [I-D.ietf-bfd-seamless-base] 205 Akiya, N., Pignataro, C., Ward, D., Bhatia, M., and J. 206 Networks, "Seamless Bidirectional Forwarding Detection 207 (S-BFD)", draft-ietf-bfd-seamless-base-09 (work in 208 progress), April 2016. 210 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 211 Requirement Levels", BCP 14, RFC 2119, 212 DOI 10.17487/RFC2119, March 1997, 213 . 215 [RFC3438] Townsley, W., "Layer Two Tunneling Protocol (L2TP) 216 Internet Assigned Numbers Authority (IANA) Considerations 217 Update", BCP 68, RFC 3438, DOI 10.17487/RFC3438, December 218 2002, . 220 [RFC3931] Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed., 221 "Layer Two Tunneling Protocol - Version 3 (L2TPv3)", 222 RFC 3931, DOI 10.17487/RFC3931, March 2005, 223 . 225 7.2. Informative References 227 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 228 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 229 . 231 Authors' Addresses 233 Vengada Prasad Govindan 234 Cisco Systems, Inc. 236 Email: venggovi@cisco.com 238 Carlos Pignataro 239 Cisco Systems, Inc. 241 Email: cpignata@cisco.com