Internet DRAFT - draft-ietf-l2tpext-sbfd-discriminator
draft-ietf-l2tpext-sbfd-discriminator
Networking Working Group V. Govindan
Internet-Draft C. Pignataro
Intended status: Standards Track Cisco
Expires: October 17, 2016 April 15, 2016
Advertising Seamless Bidirectional Forwarding Detection (S-BFD)
Discriminators in Layer Two Tunneling Protocol, Version 3 (L2TPv3)
draft-ietf-l2tpext-sbfd-discriminator-05
Abstract
This document defines a new Attribute 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 Tunneling Protocol, 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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on October 17, 2016.
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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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. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
6. Contributing Authors . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
[I-D.ietf-bfd-seamless-base] defines a simplified mechanism to use
Bidirectional Forwarding Detection (BFD) [RFC5880], referred to as
Seamless Bidirectional Forwarding Detection (S-BFD). The S-BFD
mechanisms depend on network nodes knowing the BFD discriminators
which 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 Layer Two Tunneling Protocol, Version 3 (L2TPv3)
[RFC3931] is one possible means of advertising these discriminators.
This document specifies the encoding to be used when S-BFD
discriminators 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]) and L2TPv3 (see Section 1.3 of
[RFC3931]).
2. S-BFD Target Discriminator ID AVP
The "S-BFD Target Discriminator ID" AVP is exchanged using the ICRQ
(Incoming-Call-Request), ICRP (Incoming-Call-Reply), OCRQ (Outgoing-
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Call-Request), and OCRP (Outgoing-Call-Reply) control messages during
session negotiations.
2.1. Encoding Format
The S-BFD Target Discriminator Identifier (ID) Attribute Value Pair
(AVP), Attribute Type "TBA by IANA", is an identifier used to
advertise the S-BFD Target Discriminator(s) supported by an LCCE for
the S-BFD Reflector operation. This AVP indicates that the
advertiser implements an S-BFD reflector supporting the specified
target discriminator(s) and is ready for S-BFD Reflector 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 Discriminator Advertisement AVP in a
L2TP Control Protocol 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] concerns itself with
the advertisement of only one discriminator unless the mapping to
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 ID AVP, 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 S-BFD Discriminator is associated with the L2TPv3
Session. When multiple S-BFD discriminators are advertised 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:
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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 L2TP Control Protocol Message (ICRQ, ICRP, OCRQ,
OCRP) [RFC3931] MUST NOT be set inside the S-BFD Target Discriminator
ID AVP advertisement.
3. IANA Considerations
IANA maintains a sub-registry "Message Type AVP (Attribute Type 0)
Values" in the "Control Message Attribute Value Pairs" as per
[RFC3438]. IANA is requested to assign the first free value from
this sub-registry as the Message typ AVP for "S-BFD Target
Discriminator ID".
A summary of the new AVPs requested for Attribute Type 0 follows:
Control Message Attribute Value Pairs
Attribute
Type Description
----------- ------------------
TBA by IANA S-BFD Target Discriminator ID
4. Security Considerations
Security concerns for L2TP are addressed in [RFC3931]. Introduction
of the S-BFD Discriminator Advertisement AVP introduces no new
security risks for L2TP.
Advertisement of the S-BFD discriminators does make 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].
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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. References
7.1. 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. 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>.
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Authors' Addresses
Vengada Prasad Govindan
Cisco Systems, Inc.
Email: venggovi@cisco.com
Carlos Pignataro
Cisco Systems, Inc.
Email: cpignata@cisco.com
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