Network Working Group A. Lindem (Editor)
Internet-Draft N. Shen
Expires: June 3, 2006 J. Vasseur
Cisco Systems
R. Aggarwal
Juniper Networks
S. Shaffer
BridgePort Networks
November 30, 2005
Extensions to OSPF for Advertising Optional Router Capabilities
draft-ietf-ospf-cap-08.txt
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Copyright (C) The Internet Society (2005).
Abstract
It is useful for routers in an OSPFv2 or OSPFv3 routing domain to
know the capabilities of their neighbors and other routers in the
routing domain. This draft proposes extensions to OSPFv2 and OSPFv3
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for advertising optional router capabilities. A new Router
Information (RI) LSA is proposed for this purpose. In OSPFv2, the RI
LSA will be implemented with a new opaque LSA type ID. In OSPFv3,
the RI LSA will be implemented with a new LSA type function code. In
both protocols, the RI LSA can be advertised at any of the defined
flooding scopes (link, area, or AS).
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Requirements notation . . . . . . . . . . . . . . . . . . 3
2. OSPF Router Information (RI) LSA . . . . . . . . . . . . . . . 4
2.1 OSPFv2 Router Information (RI) Opaque LSA . . . . . . . . 4
2.2 OSPFv3 Router Information (RI) Opaque LSA . . . . . . . . 5
2.3 OSPF Router Informational Capabilities TLV . . . . . . . . 5
2.4 Assigned OSPF Router Informational Capability Bits . . . . 6
2.5 Flooding Scope of the Router Information LSA . . . . . . . 7
3. Router Information LSA Opaque Usage and Applicability . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1 Normative References . . . . . . . . . . . . . . . . . . . 11
6.2 Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 11
A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . 14
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1. Introduction
It is useful for routers in an OSPFv2 [OSPF] or OSPFv3 [OSPFV3]
routing domain to know the capabilities of their neighbors and other
routers in the routing domain. This can be useful for both the
advertisement and discovery of OSPFv2 and OSPFv3 capabilities.
Throughout this document, OSPF will be used when the specification is
applicable to both OSPFv2 and OSPFv3. Similarly, OSPFv2 or OSPFv3
will be used when the text is protocol specific.
OSPF uses the options field in LSAs and hello packets to advertise
optional router capabilities. In the case of OSPFv2, all the bits in
this field have been allocated and there is no way to advertise new
optional capabilities. This document proposes extensions to OSPF to
advertise these optional capabilities via opaque LSAs in OSPFv2 and
new LSAs in OSPFv3. For existing OSPF capabilities, backward
compatibility issues dictate that this advertisement is used
primarily for informational purposes. For future OSPF features, this
advertisement MAY be used as the sole mechanism for advertisement and
discovery.
1.1 Requirements notation
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 RFC2119 [RFC2119].
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2. OSPF Router Information (RI) LSA
OSPF routers MAY optionally advertise their optional capabilities in
a link-scoped, area-scoped, or AS-scoped LSA. For existing OSPF
capabilities, this advertisement will be used primarily for
informational purposes. Future OSPF features could use the RI LSA as
the sole mechanism for advertisement and discovery. The RI LSA will
be originated initially when an OSPF router instance is created and
whenever one of the advertised capabilities is configured or changed.
2.1 OSPFv2 Router Information (RI) Opaque LSA
OSPFv2 routers will advertise a link scoped, area-scoped, or AS-
scoped Opaque-LSA [OPAQUE]. The OSPFv2 Router Information LSA has an
Opaque type of 4 and Opaque ID of 0.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 9, 10 or 11 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- TLVs -+
| ... |
The format of the TLVs within the body of an RI LSA is the same as
the format used by the Traffic Engineering Extensions to OSPF [TE].
The LSA payload consists of one or more nested Type/Length/Value
(TLV) triplets. The format of each TLV is:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The Length field defines the length of the value portion in octets
(thus a TLV with no value portion would have a length of zero). The
TLV is padded to four-octet alignment; padding is not included in
the length field (so a three octet value would have a length of
three, but the total size of the TLV would be eight octets). Nested
TLVs are also 32-bit aligned. For example, a one byte value would
have the length field set to 1, and three octets of padding would be
added to the end of the value portion of the TLV. Unrecognized types
are ignored.
2.2 OSPFv3 Router Information (RI) Opaque LSA
The OSPFv3 Router Information LSA has a function code of 12 while the
S1/S2 bit are dependent on the desired flooding scope for the LSA.
The U bit will be set indicating the OSPFv3 RI LSA should be flooded
even if it is not understood. The Link State ID (LSID) value for
this LSA is 0. This is unambiguous since an OSPFv3 router will only
advertise a single RI LSA per flooding scope.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age |1|S12| 12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 (Link State ID) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- TLVs -+
| ... |
The format of the TLVs within the body of an RI LSA as defined in
Section 2.1
When a new Router Information LSA TLV is defined, the specification
MUST explicitly state whether the TLV is applicable to OSPFv2 only,
OSPFv3 only, or both OSPFv2 and OSPFv3.
2.3 OSPF Router Informational Capabilities TLV
The first defined TLV in the body of an RI LSA is the Router
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Informational Capabilities TLV. A router advertising an RI LSA MAY
include the Router Informational Capabilities TLV. If included, it
MUST be the first TLV in the LSA. Additionally, the TLV MUST
accurately reflect the OSPF router's capabilities in the scope
advertised. However, the informational capabilities advertised have
no impact on the OSPF's operation - they are advertised purely for
informational purposes
The format of the Router Informational Capabilities 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Informational Capabilities |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type A 16 bit field set to 1.
Length A 16 bit field that indicates the length of the value
portion in octets and will be a multiple of 4 octets
dependent on the number of capabilities advertised.
Initially, the length will be 4 denoting 4 octets of
informational capability bits.
Value A variable length sequence of capability bits rounded
to a multiple of 4 octets padded with undefined bits.
Initially, there are 4 octets of capability bits.
The Router Informational Capabilities TLV MAY be followed by optional
TLVs that further specify a capability.
2.4 Assigned OSPF Router Informational Capability Bits
The following informational capability bits assigned:
Bit Capabilities
1 OSPF graceful restart capable [GRACE]
2 OSPF graceful restart helper [GRACE]
3 OSPF Stub Router support [STUB]
4 OSPF Traffic Engineering support [TE]
5 OSPF point-to-point over LAN [P2PLAN]
6 OSPF Experimental TE [EXPTE]
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7-31 Future assignments
2.5 Flooding Scope of the Router Information LSA
The flooding scope for a Router Information LSA is determined by the
LSA type. For OSPFv2, type 9 (link-scoped), type 10 (area-scoped),
or a type 11 (AS-scoped) opaque LSA may be flooded. For OSPFv3, the
flooding scope is determined by the S1 and S2 bits in the LSA type.
If AS wide flooding scope is chosen, the originating router should
also advertise area scoped LSA(s) into any attached NSSA area(s). An
OSPF router MAY advertise different capabilities when both NSSA area
scoped LSA(s) and an AS scoped LSA is advertised. This allows
functional capabilities to be limited in scope. For example, a
router may be an area border router but only support traffic
engineering (TE) in a subset of its attached areas.
The choice of flooding scope is made by the advertising router and is
a matter of local policy. The originating router MAY advertise
multiple RI LSAs as long as the flooding scopes differ. TLV flooding
scope rules will be specified on a per-TLV basis and MUST be
specified in the accompanying specifications for new Router
Information LSA TLVs.
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3. Router Information LSA Opaque Usage and Applicability
The purpose of the Router Information (RI) LSA is to advertise
information relating to the aggregate OSPF router. Normally, this
should be confined to TLVs with a single value or very few values.
It is not meant to be a generic container to carry any and all
information. The intent is to both limit the size of the RI LSA to
the point where an OSPF router will always be able to contain the
TLVs in a single LSA and to keep the task of determining what has
changed between LSA instances reasonably simple. Hence, discretion
and sound engineering judgment MUST be adhered to when deciding
whether newly proposed TLV(s) in support of a new application are
advertised in the RI LSA or warrant the creation of an application
specific LSA.
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4. Security Considerations
The function described in this document does not create any new
security issues for the OSPF protocol. Security considerations for
the base OSPF protocol are covered in [OSPF] and [OSPFV3].
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5. IANA Considerations
The following IANA assignments are to be made from existing
registries:
1. The OSPFv2 opaque LSA type 4 will need to be reserved for the
OSPFv2 RI opaque LSA.
2. The OSPFv3 LSA type function code 18 will need to be reserved for
the OSPFv3 RI LSA.
New registries are defined for the following purposes:
1. Registry for OSPF RI TLVs - The value of 1 for the capabilities
TLV is defined herein. All TLV additions are subject to OSPF WG
review.
2. Registry for OSPF Router Informational Capability Bits - The
values defined in Section 2.3. All Router Informational
Capability TLV additions are subject to OSPF WG review.
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6. References
6.1 Normative References
[OPAQUE] Coltun, R., "The OSPF Opaque LSA Option", RFC 2370,
July 1998.
[OSPF] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[OSPFV3] Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6",
RFC 2740, December 1999.
[RFC2119] Bradner, S., "Key words for use in RFC's to Indicate
Requirement Levels", RFC 2119, March 1997.
[TE] Katz, D., Yeung, D., and K. Kompella, "Traffic Engineering
Extensions to OSPF", RFC 3630, September 2003.
6.2 Informative References
[EXPTE] Srisuresh, P. and P. Joseph, "OSPF OSPF-TE: An
experimental extension to OSPF for Traffic Engineering",
draft-srisuresh-ospf-te-07.txt (work in progress).
[GRACE] Moy, J., Pillay-Esnault, P., and A. Lindem, "Graceful OSPF
Restart", RFC 3623, November 2003.
[P2PLAN] Shen, N. and A. Zinin, "Point-to-point operation over LAN
in link-state routing protocols",
draft-ietf-isis-igp-p2p-over-lan-05.txt (work in progress).
[STUB] Retana, A., Nguyen, L., White, R., Zinin, A., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 3137,
June 2001.
Authors' Addresses
Acee Lindem
Cisco Systems
7025 Kit Creek Road
Research Triangle Park, NC 27709
USA
Email: acee@cisco.com
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Naiming Shen
Cisco Systems
225 West Tasman Drive
San Jose, CA 95134
USA
Email: naiming@cisco.com
Jean-Philippe Vasseur
Cisco Systems
300 Beaver Brook Road
Boxborough, MA 01719
USA
Email: jpv@cisco.com
Rahul Aggarwal
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
USA
Email: rahul@juniper.net
Scott Shaffer
BridgePort Networks
One Main Street, 7th Floor
Cambridge, MA 02142
USA
Email: sshafferl@bridgeport-networks.com
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Appendix A. Acknowledgments
The idea for this work grew out of a conversation with Andrew Partan
and we would like to thank him for his contribution. The authors
would like to thanks Peter Psenak for his review and helpful comments
on early versions of the draft.
Comments from Abhay Roy, Vishwas Manral, Vivek Dubey, and Adrian
Farrel have been incorporated into later draft versions.
The RFC text was produced using Marshall Rose's xml2rfc tool.
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