Networking Working GroupInternet Engineering Task Force (IETF) V. GovindanInternet-DraftRequest for Comments: 7886 C. PignataroIntended status:Category: Standards Track CiscoExpires: October 17, 2016 April 15,ISSN: 2070-1721 June 2016 Advertising Seamless Bidirectional Forwarding Detection (S-BFD) Discriminators in the Layer Two TunnelingProtocol,Protocol Version 3 (L2TPv3)draft-ietf-l2tpext-sbfd-discriminator-05Abstract This document defines a newAttribute ValueAttribute-Value Pair (AVP) that allows L2TP Control Connection Endpoints (LCCEs) to advertise one or more Seamless Bidirectional Forwarding Detection (S-BFD) Discriminator values using the Layer Two TunnelingProtocol, VersionProtocol version 3 (L2TPv3).Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].Status of This Memo ThisInternet-Draftissubmitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documentsan Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF).Note that other groups may also distribute working documents as Internet-Drafts. The listIt represents the consensus ofcurrent Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents validthe IETF community. It has received public review and has been approved fora maximumpublication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status ofsix monthsthis document, any errata, and how to provide feedback on it may beupdated, replaced, or obsoleted by other documentsobtained atany time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on October 17, 2016.http://www.rfc-editor.org/info/rfc7886. Copyright Notice Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 2. S-BFD Target Discriminator ID AVP . . . . . . . . . . . . . . 2 2.1. Encoding Format . . . . . . . . . . . . . . . . . . . . . 3 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5.AcknowledgementsReferences . . . . . . . . . . . . . . . . . . . . . .5 6. Contributing Authors. . . 4 5.1. Normative References . . . . . . . . . . . . . . . . .5 7.. 4 5.2. Informative References . . . . . . . . . . . . . . . . . 5 Acknowledgements . . . . . . . .5 7.1. Normative References. . . . . . . . . . . . . . . . 5 Contributors . . . . . . . . .5 7.2. Informative References. . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . .65 1. Introduction[I-D.ietf-bfd-seamless-base][RFC7880] defines a simplified mechanism to use Bidirectional Forwarding Detection (BFD) [RFC5880], referred to as Seamless Bidirectional Forwarding Detection (S-BFD). The S-BFDmechanisms dependmechanism depends on network nodes knowing the BFDdiscriminators whichDiscriminators that each node in the network has reserved for this purpose. S-BFD requires the usage of unique discriminators within an administrative domain. The use of the Layer Two TunnelingProtocol, VersionProtocol version 3 (L2TPv3) [RFC3931] is one possible means of advertising these discriminators. This document specifies the encoding to be used when S-BFDdiscriminatorsDiscriminators are advertised using L2TPv3. 1.1. Terminology The reader is expected to be very familiar with the terminology and protocol constructs defined in S-BFD (see Section 2 of[I-D.ietf-bfd-seamless-base])[RFC7880]) and L2TPv3 (see Section 1.3 of [RFC3931]). The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 2. S-BFD Target Discriminator ID AVP The"S-BFDS-BFD Target DiscriminatorID" AVPIdentifier (ID) Attribute Value Pair (AVP) is exchanged using the ICRQ (Incoming-Call-Request), ICRP (Incoming-Call-Reply), OCRQ(Outgoing- Call-Request),(Outgoing-Call-Request), and OCRP (Outgoing-Call-Reply) control messages during sessionnegotiations.negotiation. 2.1. Encoding Format The S-BFD Target DiscriminatorIdentifier (ID) Attribute Value Pair (AVP),ID AVP, Attribute Type"TBA by IANA",102, is an identifier used to advertise the S-BFDTarget Discriminator(s)target discriminator(s) supported by anLCCEL2TP Control Connection Endpoint (LCCE) for the S-BFDReflectorreflector operation. This AVP indicates that the advertiser implements an S-BFD reflector supporting the specified target discriminator(s) and is ready for S-BFDReflectorreflector operation. The receiving LCCE MAY use this AVP if it wants to monitor connectivity to the advertising LCCE using S-BFD. The Attribute Value field for this AVP has the following format: S-BFD Target Discriminator ID (ICRQ, ICRP, OCRQ, OCRP): No. of octets +-----------------------------+ | Discriminator Value(s) | 4/Discriminator : : +-----------------------------+ An LCCE MAY include the S-BFD Target DiscriminatorAdvertisementID AVP advertisement inaan L2TPControl Protocolcontrol message (ICRQ, ICRP, OCRQ, OCRP) [RFC3931]. If the other LCCE does not wish to monitor connectivity using S-BFD, it MAY safely discard this AVP without affecting the rest of session negotiation. While[I-D.ietf-bfd-seamless-base][RFC7880] concerns itself with the advertisement of only one discriminator unless the mappingtoof discriminators to entities is specified, the AVP encoding allows the specification of an arbitrary number of S-BFD Discriminators (at least one) for extensibility. When an LCCE uses the S-BFD Target Discriminator IDAVP,AVP advertisement, multiple S-BFD Discriminators MAY be included, and at least one S-BFD Discriminator MUST be included. When one S-BFD Discriminator is advertised, such an S-BFD Discriminator is associated with the L2TPv3Session.session. When multiple S-BFDdiscriminatorsDiscriminators areadvertisedadvertised, how a given discriminator is mapped to a specific use case is out of scope for this document. The S-BFD Target Discriminator ID AVP allows for advertising at least one S-BFD Discriminator value: 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Discriminator 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Discriminator 2 (Optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Discriminator n (Optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The M bit of the L2TPControl Protocol Messagecontrol message (ICRQ, ICRP, OCRQ, OCRP) [RFC3931] MUST NOT be set inside the S-BFD Target Discriminator IDAVP advertisement.AVP. 3. IANA Considerations IANA maintainsa sub-registry "Message Type AVP (Attribute Type 0) Values" inthe "Control Message Attribute Value Pairs" sub-registry as per [RFC3438]. IANAis requested to assignhas assigned thefirst freefollowing valuefrom this sub-registry asto theMessage typ AVP for "S-BFDS-BFD Target DiscriminatorID". A summary of the new AVPs requested for Attribute Type 0 follows:ID: Control Message Attribute Value Pairs Attribute Type Description ----------- ------------------TBA by IANA102 S-BFD Target Discriminator ID 4. Security Considerations Security concerns for L2TP are addressed in [RFC3931].IntroductionThe introduction of the S-BFD Target DiscriminatorAdvertisementID AVP advertisement introduces no new security risks for L2TP.Advertisement ofAdvertising the S-BFDdiscriminators does makeDiscriminators makes it possible for attackers to initiate S-BFD sessions using the advertised information. The vulnerabilities this poses and how to mitigate them are discussed in the Security Considerations section of[I-D.ietf-bfd-seamless-base].[RFC7880]. 5.Acknowledgements Authors would like to thank Nobo Akiya, Stewart Bryant and Pawel Sowinski for providing core inputs for the document and for performing thorough reviews and providing number of comments. Authors would like to thank Nagendra Kumar for his reviews. 6. Contributing Authors Mallik Mudigonda Cisco Systems, Inc. Email: mmudigon@cisco.com 7.References7.1.5.1. Normative References[I-D.ietf-bfd-seamless-base] Akiya, N., Pignataro, C., Ward, D., Bhatia, M., and J. Networks, "Seamless Bidirectional Forwarding Detection (S-BFD)", draft-ietf-bfd-seamless-base-09 (work in progress), April 2016.[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>. [RFC3438] Townsley, W., "Layer Two Tunneling Protocol (L2TP) Internet Assigned Numbers Authority (IANA) Considerations Update", BCP 68, RFC 3438, DOI 10.17487/RFC3438, December 2002, <http://www.rfc-editor.org/info/rfc3438>. [RFC3931] Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed., "Layer Two Tunneling Protocol - Version 3 (L2TPv3)", RFC 3931, DOI 10.17487/RFC3931, March 2005, <http://www.rfc-editor.org/info/rfc3931>.7.2.[RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S. Pallagatti, "Seamless Bidirectional Forwarding Detection (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, June 2016, <http://www.rfc-editor.org/info/rfc7880>. 5.2. Informative References [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, <http://www.rfc-editor.org/info/rfc5880>. Acknowledgements The authors would like to thank Nobo Akiya, Stewart Bryant, and Pawel Sowinski for providing core inputs for the document, performing thorough reviews, and providing a number of comments. The authors would also like to thank Nagendra Kumar for his reviews. Contributors Mallik Mudigonda Cisco Systems, Inc. Email: mmudigon@cisco.com Authors' Addresses Vengada Prasad Govindan Cisco Systems, Inc. Email: venggovi@cisco.com Carlos Pignataro Cisco Systems, Inc. Email: cpignata@cisco.com