Internet DRAFT - draft-bhatia-ospf-sbfd-discriminator
draft-bhatia-ospf-sbfd-discriminator
Internet Engineering Task Force M. Bhatia
Internet-Draft T. Ranganath
Intended status: Standards Track Alcatel-Lucent
Expires: November 9, 2014 C. Pignataro
Cisco Systems
S. Aldrin
Huawei Technologies
May 8, 2014
OSPF extensions to advertise S-BFD Target Discriminator
draft-bhatia-ospf-sbfd-discriminator-00
Abstract
This document defines a new OSPF Router Information (RI) TLV that
allows OSPF routers to flood the S-BFD discriminator values
associated with a target network identifier. This mechanism is
applicable to both OSPFv2 and OSPFv3.
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 November 9, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Relationship between OSPF and S-BFD . . . . . . . . . . . 2
2. Implementation . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. S-BFD Discriminator TLV . . . . . . . . . . . . . . . . . 3
2.2. Flooding Scope . . . . . . . . . . . . . . . . . . . . . 3
3. Backward Compatibility . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Seamless Bidirectional Forwarding Detection (S-BFD), specified in
[I-D.akiya-bfd-seamless-base], is a simplified mechanism for using
BFD with many negotiations eliminated. This is achieved by using
unique network-wide discriminators to identify the Network Targets
(e.g., IP addresses). These S-BFD discriminators can be advertised
by the IGPs, and this document concerns itself with OSPF.
Specifically, this document defines a new TLV (named the S-BFD
Discriminator TLV) to be carried within the OSPF Router Information
LSA ([RFC4970]).
1.1. Relationship between OSPF and S-BFD
This document, implicitly, defines a relationship between OSPF and
S-BFD. S-BFD assigns one or more Discriminators to each S-BFD
reflector node. OSPF, in turn, learns about these from S-BFD, and
floods them in the newly defined TLV. After this information is
flooded, it is stored in all the OSPF nodes such that S-BFD
initiators can map out target nodes to target Discriminators, and can
therefore construct the S-BFD probe.
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2. Implementation
This extension makes use of the Router Information (RI) Opaque LSA,
defined in [RFC4970] , for both OSPFv2 [RFC2328] and OSPFv3
[RFC5340], by defining a new OSPF Router Information (RI) TLV: the
S-BFD Discriminator TLV.
The S-BFD Discriminator TLV is OPTIONAL. Upon receipt of the TLV, a
router may decide to ignore this TLV or install the S-BFD
discriminator in BFD Target Identifier Table.
2.1. S-BFD Discriminator TLV
The format of the S-BFD Discriminator TLV is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator 2 (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator n (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type - S-BFD Discriminator TLV Type
Length - Total length of the discriminator (Value field) in octets,
not including the optional padding. The Length is a multiple of 4
octets, and consequently specifies how many Discriminators are
included in the TLV.
Value - S-BFD network target discriminator value or values.
Routers that do not recognize the S-BFD Discriminator TLV Type MUST
ignore the TLV. S-BFD discriminator is associated with the BFD
Target Identifier type, that allows demultiplexing to a specific task
or service.
2.2. Flooding Scope
The flooding scope for S-BFD Discriminator information advertised
through OSPF can be limited to one or more OSPF areas, or can be
extended across the entire OSPF routing domain.
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Note that the S-BFD session may be required to pan multiple areas, in
which case the flooding scope may comprise these areas. This could
be the case for an ABR, for instance, advertising the S-BFD
Discriminator information within the backbone area and/or a subset of
its attached IGP area(s).
The S-BFD Discriminator TLV is advertised within OSPFv2 Router
Information LSAs (Opaque type of 4 and Opaque ID of 0) or OSPFv3
Router Information LSAs (function code of 12), which are defined in
[RFC4970]. As such, elements of procedure are inherited from those
defined in [RFC4970].
In OSPFv2, the flooding scope is controlled by the opaque LSA type
(as defined in [RFC5250]) and in OSPFv3, by the S1/S2 bits (as
defined in [RFC5340]). If the flooding scope is area local, then the
S-BFD Discriminator TLV MUST be carried within an OSPFv2 type 10
router information LSA or an OSPFV3 Router Information LSA with the
S1 bit set and the S2 bit clear. If the flooding scope is the entire
IGP domain, then the S-BFD Discriminator TLV MUST be carried within
an OSPFv2 type 11 Router Information LSA or OSPFv3 Router Information
LSA with the S1 bit clear and the S2 bit set.
When the S-BFD Reflector is deactivated, the OSPF speaker advertising
this S-BFD Discriminator MUST originate a new Router Information LSA
that no longer includes the corresponding S-BFD Discriminator TLV,
provided there are other TLVs in the LSA. If there are no other TLVs
in the LSA, it MUST either send an empty Router Information LSA or
purge it by prematurely ageing it.
For intra-area reachability, the S-BFD Discriminator TLV information
regarding a specific target identifier is only considered current and
useable when the router advertising this information is itself
reachable via OSPF calculated paths in the same area of the LSA in
which the S-BFD Discriminator TLV appears. In the case of domain-
wide flooding, i.e., where the originator is sitting in a remote
area, the mechanism described in section 5 of [RFC5250] should be
used.
A change in information in the S-BFD Discriminator TLV MUST NOT
trigger any SPF computation at a receiving router.
3. Backward Compatibility
The S-BFD Discriminator TLV defined in this document does not
introduce any interoperability issues.
A router not supporting the S-BFD Discriminator TLV will just
silently ignore the TLV as specified in [RFC4970].
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4. Security Considerations
This document defines OSPF extensions to distribute the S-BFD
discriminator within an administrative domain. Hence the security of
the S-BFD discriminator distribution relies on the security of OSPF.
OSPF provides no encryption mechanism for protecting the privacy of
LSAs and, in particular, the privacy of the S-BFD discriminator
advertisement information. This however is not a concern as there
isn't any need to hide the discriminator value that can be used to
reach the Reflectors.
5. IANA Considerations
IANA has defined a registry for TLVs carried in the Router
Information LSA defined in [RFC4970]. IANA needs to assign a new TLV
codepoint for the S-BFD Discriminator TLV carried within the Router
Information LSA.
Value TLV Name Reference
----- -------- ----------
TBD S-BFD (this document)
Discriminator
6. Acknowledgements
The authors would like to thank Nobo Akiya, Les Ginsberg, Mach Chen
and Peter Psenak for insightful comments and useful suggestions.
7. References
7.1. Normative References
[I-D.akiya-bfd-seamless-base]
Akiya, N., Pignataro, C., Ward, D., Bhatia, M., and J.
Networks, "Seamless Bidirectional Forwarding Detection
(S-BFD)", draft-akiya-bfd-seamless-base-03 (work in
progress), April 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S.
Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 4970, July 2007.
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[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
7.2. Informative References
[RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
OSPF Opaque LSA Option", RFC 5250, July 2008.
Authors' Addresses
Manav Bhatia
Alcatel-Lucent
Email: manav.bhatia@alcatel-lucent.com
Trilok Ranganath
Alcatel-Lucent
Email: trilok.ranganatha@alcatel-lucent.com
Carlos Pignataro
Cisco Systems
Email: cpignata@cisco.com
Sam Aldrin
Huawei Technologies
Email: aldrin.ietf@gmail.com
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