Internet DRAFT - draft-ietf-ospf-sbfd-discriminator
draft-ietf-ospf-sbfd-discriminator
Internet Engineering Task Force C. Pignataro
Internet-Draft Cisco
Intended status: Standards Track M. Bhatia
Expires: October 31, 2016 Ionos Networks
S. Aldrin
Huawei Technologies
T. Ranganath
Nokia
April 29, 2016
OSPF Extensions to Advertise Seamless Bidirectional Forwarding Detection
(S-BFD) Target Discriminators
draft-ietf-ospf-sbfd-discriminator-06
Abstract
This document defines a new OSPF Router Information (RI) TLV that
allows OSPF routers to flood the Seamless Bidirectional Forwarding
Detection (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.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 31, 2016.
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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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Relationship Between OSPF and S-BFD . . . . . . . . . . . 3
2. Implementation . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. S-BFD Discriminator TLV . . . . . . . . . . . . . . . . . 3
2.2. Flooding Scope . . . . . . . . . . . . . . . . . . . . . 4
3. Backward Compatibility . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Seamless Bidirectional Forwarding Detection (S-BFD), specified in
[I-D.ietf-bfd-seamless-base], is a simplified mechanism for using
Bidirectional Forwarding Detection (BFD) with many negotiations
eliminated. This is achieved by using four-octet discriminators,
unique within an administrative domain, to identify the Network
Targets. 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 (RI) Link State
Advertisement (LSA) ([RFC7770]).
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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.
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.
2. Implementation
This extension makes use of the Router Information (RI) Opaque LSA,
defined in [RFC7770] , 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 install the S-BFD discriminator in BFD Target
Identifier Table.
In the presence of multiple instances of the OSPF/OSPFv3 RI LSA, the
S-BFD discriminators for an OSPF router are the union of all
discriminators advertised in all instances of the S-BFD Discriminator
TLV (see Section 2.1) in all advertised non-MaxAge OSPF RI LSAs.
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type - S-BFD Discriminator TLV Type (TBD [to be filled in by IANA])
Length - Total length of the discriminator(s) that appear in the
Value field, in octets. Each discriminator is 4 octets, so the
Length is 4 times the number of discriminators included in the TLV.
There is no optional padding for this field.
Discriminator(s) - The Value field of the TVL includes the S-BFD
network target discriminator value or values.
Routers that do not recognize the S-BFD Discriminator TLV Type will
ignore the TLV [RFC7770], and therefore will not learn S-BFD
discriminators via OSPF.
2.2. Flooding Scope
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
[RFC7770]. As such, elements of procedure are inherited from those
defined in [RFC7770].
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.
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Although the S-BFD discriminators may change when enabling the S-BFD
functionality or via an explicit configuration event, such changes
are expected to occur very rarely. Such a change in the information
will require S-BFD Discriminator TLV in OSPF to be advertised.
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 [RFC7770].
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 [RFC7770]. 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.
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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>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<http://www.rfc-editor.org/info/rfc2328>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<http://www.rfc-editor.org/info/rfc5340>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <http://www.rfc-editor.org/info/rfc7770>.
7.2. Informative References
[RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250,
July 2008, <http://www.rfc-editor.org/info/rfc5250>.
Authors' Addresses
Carlos Pignataro
Cisco Systems, Inc.
Email: cpignata@cisco.com
Manav Bhatia
Ionos Networks
Email: manav@ionosnetworks.com
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Sam Aldrin
Huawei Technologies
Email: aldrin.ietf@gmail.com
Trilok Ranganath
Nokia
Email: trilok.ranganatha@nokia.com
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