RFC 7883 PROPOSED STANDARD IS-IS · BFD · ROUTING
Advertising Seamless Bidirectional Forwarding Detection (S-BFD) Discriminators in IS-IS
An IS-IS Router CAPABILITY sub-TLV advertises S-BFD discriminator values.
RFC EDITOR
Ginsberg, L., Akiya, N., and M. Chen, "Advertising Seamless Bidirectional Forwarding Detection (S-BFD) Discriminators in IS-IS", RFC 7883, DOI 10.17487/RFC7883, July 2016, <https://www.rfc-editor.org/info/rfc7883>.
BIBTEX
@misc{rfc7883,
series = {Request for Comments},
number = 7883,
howpublished = {RFC 7883},
publisher = {RFC Editor},
doi = {10.17487/RFC7883},
url = {https://www.rfc-editor.org/info/rfc7883},
author = {L. Ginsberg and N. Akiya and M. Chen},
title = {{Advertising Seamless Bidirectional Forwarding Detection (S-BFD) Discriminators in IS-IS}},
pagetotal = 5,
year = 2016,
month = jul,
} RFC text
Contents
Internet Engineering Task Force (IETF) L. Ginsberg
Request for Comments: 7883 Cisco Systems
Category: Standards Track N. Akiya
ISSN: 2070-1721 Big Switch Networks
M. Chen
Huawei
July 2016
Advertising Seamless Bidirectional Forwarding Detection (S-BFD)
Discriminators in IS-IS
Abstract
This document defines a means of advertising one or more Seamless
Bidirectional Forwarding Detection (S-BFD) Discriminators using the
IS-IS Router CAPABILITY TLV.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7883.
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.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction ....................................................3
2. Encoding Format .................................................3
3. IANA Considerations .............................................4
4. Security Considerations .........................................4
5. Normative References ............................................4
Acknowledgements ...................................................5
Authors' Addresses .................................................5
1. Introduction
[RFC7880] defines a simplified mechanism for using Bidirectional
Forwarding Detection (BFD) [RFC5880]. This mechanism depends on
network nodes knowing the BFD Discriminators that each node in the
network has reserved for this purpose. The use of the Intermediate
System to Intermediate System (IS-IS) [IS-IS] protocol is one
possible means of advertising these discriminators.
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. Encoding Format
The IS-IS Router CAPABILITY TLV as defined in [RFC4971] will be used
to advertise Seamless BFD (S-BFD) Discriminators. A new sub-TLV is
defined as described below. S-BFD Discriminators sub-TLVs are
formatted as specified in [RFC5305].
No. of octets
+-----------------------------+
| Type (20) | 1
+-----------------------------+
| Length (multiple of 4) | 1
+-----------------------------+
| Discriminator Value(s) | 4/Discriminator
: :
+-----------------------------+
The inclusion of an S-BFD Discriminators sub-TLV in a Router
CAPABILITY TLV is optional. Multiple S-BFD Discriminators sub-TLVs
MAY be advertised by an IS. How a given discriminator is mapped to a
specific use case when multiple S-BFD Discriminators are advertised
is out of scope for this document.
S-BFD Discriminator advertisements MAY be flooded within an area or
throughout the domain, using the procedures specified in [RFC4971].
The appropriate flooding scope depends on the intended use of S-BFD.
If S-BFD usage will be exclusively within a Level-1 area, then area
scope is appropriate. If S-BFD usage will span different Level-1
areas, then domain scope is appropriate.
3. IANA Considerations
IANA has added a new sub-TLV in the "Sub-TLVs for TLV 242" registry.
The registration is as follows:
Value Description
----- --------------------
20 S-BFD Discriminators
4. Security Considerations
Security concerns for IS-IS are addressed in [IS-IS], [RFC5304], and
[RFC5310]. The new S-BFD Discriminators sub-TLV does not introduce
any new security risks for IS-IS.
Advertising the S-BFD Discriminators 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
[RFC7880].
5. Normative References
[IS-IS] International Organization for Standardization,
"Intermediate System to Intermediate System intra-domain
routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode network service (ISO 8473)",
ISO Standard 10589, 2002.
[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>.
[RFC4971] Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed.,
"Intermediate System to Intermediate System (IS-IS)
Extensions for Advertising Router Information", RFC 4971,
DOI 10.17487/RFC4971, July 2007,
<http://www.rfc-editor.org/info/rfc4971>.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC5304,
October 2008, <http://www.rfc-editor.org/info/rfc5304>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305,
October 2008, <http://www.rfc-editor.org/info/rfc5305>.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC5310,
February 2009, <http://www.rfc-editor.org/info/rfc5310>.
[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>.
[RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
Pallagatti, "Seamless Bidirectional Forwarding Detection
(S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
<http://www.rfc-editor.org/info/rfc7880>.
Acknowledgements
The authors wish to thank Sam Aldrin, Manav Bhatia, and Carlos
Pignataro for input essential to defining the needed functionality.
Authors' Addresses
Les Ginsberg
Cisco Systems
510 McCarthy Blvd.
Milpitas, CA 95035
United States of America
Email: ginsberg@cisco.com
Nobo Akiya
Big Switch Networks
Email: nobo.akiya.dev@gmail.com
Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com
ISO Plain Language
On this page
PROBLEMSeamless Bidirectional Forwarding Detection (S-BFD) requires nodes to know discriminators reserved by other nodes.
MECHANISMA new sub-TLV, type 20, carries one or more four-octet discriminators inside an IS-IS Router CAPABILITY TLV.
WHY IT MATTERSAn IS may flood the values within an area or throughout the domain, depending on intended S-BFD use.
§1Why Discriminators Are Advertised
RFC 7880 defines a simplified mechanism for Bidirectional Forwarding Detection called Seamless BFD (S-BFD). It depends on network nodes knowing the discriminator values that each node reserves.
This RFC defines one way to advertise those values: use the Intermediate System to Intermediate System (IS-IS) routing protocol.
S-BFD needs each node to know discriminator values reserved by other nodes. IS-IS can distribute those values through the network.
§2The Discriminator Sub-TLV
The IS-IS Router CAPABILITY TLV carries a new S-BFD Discriminators sub-TLV. Its type is 20 and takes one octet, its length takes one octet and must be a multiple of four, and its payload contains four octets per discriminator.
The sub-TLV is optional, and an IS MAY advertise several. The mapping of a discriminator to a particular use is outside this RFC's scope.
The optional field lists discriminator values, with four octets for each one. This RFC does not define what each value is used for.
§2Flooding Scope
Advertisements MAY be flooded within an IS-IS area or throughout the domain, using RFC 4971 procedures. The intended S-BFD use determines the scope.
Area scope is appropriate when use stays within a Level-1 area. Domain scope is appropriate when use spans different Level-1 areas.
Choose where the advertisement travels based on where S-BFD will be used. A local use can stay within an area; a use across areas can be flooded through the domain.
§4IANA and Security
IANA registered value 20, named S-BFD Discriminators, in the Sub-TLVs for TLV 242 registry. The new sub-TLV adds no new security risks for IS-IS.
Advertising discriminators can let attackers initiate S-BFD sessions using the advertised information. RFC 7880 discusses those vulnerabilities and mitigations.
IANA added the new sub-TLV number to its registry. Publishing discriminator values can enable attempts to start S-BFD sessions, a risk discussed in RFC 7880.
§5References
[RFC4971]RFC 4971Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed., "Intermediate System to Intermediate System (IS-IS) Extensions for Advertising Router Information", RFC 4971, July 2007.July 2007[RFC7880]RFC 7880Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S. Pallagatti, "Seamless Bidirectional Forwarding Detection (S-BFD)", RFC 7880, July 2016.July 2016