Network Working Group A. Lindem (Editor)
Internet-Draft Cisco Systems, Inc
Expires: August 8, 2005 N. Shen
Cisco Systems
R. Aggarwal
Juniper Networks
S. Shaffer
BridgePort Networks
JP. Vasseur
Cisco Systems, Inc
February 7, 2005
Extensions to OSPF for Advertising Optional Router Capabilities
draft-ietf-ospf-cap-06.txt
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Copyright (C) The Internet Society (2005).
Abstract
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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
for advertising optional router capabilities. A new Router
Information (RI) LSA is proposed for this purpose.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 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 Capabilities TLV . . . . . . . . . . . . . . . 6
2.4 Assiged OSPF Router Capability Bits . . . . . . . . . . . 7
2.5 Flooding Scope of the Router Information LSA . . . . . . . 7
3. Router Information LSA Opaque Usage and Applicability . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1 Normative References . . . . . . . . . . . . . . . . . . . . 12
6.2 Informative References . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 12
A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . 15
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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. Similiarly, 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 OSFPv2, 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. For existing OSPF
capabilities, backward compatibility issues dictate that this
advertisement is used primarily for informational purposes. For
future OSPF features, this advertimsement MAY be used as the sole
mechanism for advertisement and discovery.
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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 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- TLV's -+
| ... |
The format of the TLV's within the body of a router information 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:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
TLV's 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.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age |1|S12| 12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 (Link State ID) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- TLV's -+
| ... |
The format of the TLV's within the body of a router information 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 Capabilities TLV
The first defined TLV in the body of an RI LSA is the Router
Capabilities TLV. A router advertising an RI LSA MUST include the
Router Capabilities TLV and it MUST be the first TLV in the LSA.
Additionally, the TLV MUST accurately reflect the OSPF router's
capabilities in the scope it is advertised.
The format of the Router Capabilities TLV is as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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. In
this revision the length will be 4 denoting 4 octets of
capability bits.
Value A variable length sequence of capability flags rounded
to a multiple of 4 octects padded with undefined bits.
In this revision, there are 4 octets of capability bits.
The Router Capabilities TLV MAY be followed by optional TLV's that
further specify a capability.
2.4 Assiged OSPF Router Capability Bits
The following bits in the first capability flag have been assigned:
Bit Capabilities
0-3 Unassigned
4 OSPF graceful restart capable [GRACE]
5 OSPF graceful restart helper [GRACE]
6 OSPF Stub Router support [STUB]
7 OSPF Traffic Engineering support [TE]
8 OSPF point-to-point over LAN [P2PLAN]
9 OSPF Experimental TE [EXPTE]
10-31 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-scope), 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
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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 judgement MUST be adhered to when deciding
whether newly proposed TLV(s) in support of a new application are
advertised in the RI LSA or warrent 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].
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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 OSPFv2 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 Capability Flags - The values defined in
Section 2.3. All Router 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, April 1998.
[RFC2119] Bradner, S., "Key words for use in RFC's to Indicate
Requirement Levels", RFC 2328, March 1977.
[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.
[T3CAP] Vasseur, JP., Psenak, P., Yasukawa, S. and JL. Le Roux,
"OSPF MPLS Traffic Engineering Capabilities",
draft-vasseur-ospf-te-caps-00.txt (work in progress).
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Authors' Addresses
Acee Lindem
Cisco Systems, Inc
7025 Kit Creek Road
Research Triangle Park, NC 27709
USA
EMail: acee@cisco.com
Naiming Shen
Cisco Systems
225 West Tasman Drive
San Jose, CA 95134
USA
EMail: naiming@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
Jean-Philippe Vasseur
Cisco Systems, Inc
300 Beaver Brook Road
Boxborough, MA 01719
USA
EMail: jpv@cisco.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
early versions of the draft.
Comments from Abhay Roy, Vishwas Manral, Vivek Dubey, and Adrian
Farrel were incorporated into the final draft version.
The RFC text was produced using Marshall Rose's xml2rfc tool.
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