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IETF RFC 4970
Extensions to OSPF for Advertising Optional Router Capabilities
Last modified on Wednesday, July 18th, 2007
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Network Working Group A. Lindem, Ed.
Request for Comments: 4970 Redback Networks
Category: Standards Track N. Shen
JP. Vasseur
Cisco Systems
R. Aggarwal
Juniper Networks
S. Shaffer
BridgePort Networks
July 2007
Extensions to OSPF for Advertising Optional Router Capabilities
 Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright © The IETF Trust (2007).
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 document proposes extensions to OSPFv2 and
OSPFv3 for advertising optional router capabilities. A new Router
Information (RI) Link State Advertisement (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
autonomous system (AS)).
Lindem, et al. Standards Track PAGE 1 
RFC 4970 OSPF Capability Extensions July 2007
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 3
2. OSPF Router Information (RI) LSA . . . . . . . . . . . . . . . 3
2.1. OSPFv2 Router Information (RI) Opaque LSA . . . . . . . . 3
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 . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Normative References . . . . . . . . . . . . . . . . . . . 10
6.2. Informative References . . . . . . . . . . . . . . . . . . 10
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 11
Lindem, et al. Standards Track PAGE 2
RFC 4970 OSPF Capability Extensions July 2007
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 so new optional capabilities cannot be
advertised. 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 [RFC-KEYWORDS].
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.
Lindem, et al. Standards Track PAGE 3
RFC 4970 OSPF Capability Extensions July 2007
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 -+
| ... |
OSPFv2 Router Information Opaque LSA
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... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TLV Format
The Length field defines the length of the value portion in octets
(thus a TLV with no value portion would have a length of 0). The TLV
is padded to 4-octet alignment; padding is not included in the length
field (so a 3-octet value would have a length of 3, but the total
size of the TLV would be 8 octets). Nested TLVs are also 32-bit
aligned. For example, a 1-byte value would have the length field set
to 1, and 3 octets of padding would be added to the end of the value
portion of the TLV. Unrecognized types are ignored.
Lindem, et al. Standards Track PAGE 4
RFC 4970 OSPF Capability Extensions July 2007
2.2. OSPFv3 Router Information (RI) Opaque LSA
The OSPFv3 Router Information LSA has a function code of 12 while the
S1/S2 bits are dependent on the desired flooding scope for the LSA.
The U bit will be set indicating that 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 -+
| ... |
OSPFv3 Router Information LSA
The format of the TLVs within the body of an RI LSA is 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
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 protocol's operation -- they are advertised
purely for informational purposes.
Lindem, et al. Standards Track PAGE 5
RFC 4970 OSPF Capability Extensions July 2007
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. Bits
are numbered left-to-right starting with the most
significant bit being bit 0.
OSPF Router Informational Capabilities TLV
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 are assigned:
Bit Capabilities
0 OSPF graceful restart capable [GRACE]
1 OSPF graceful restart helper [GRACE]
2 OSPF Stub Router support [STUB]
3 OSPF Traffic Engineering support [TE]
4 OSPF point-to-point over LAN [P2PLAN]
5 OSPF Experimental TE [EXP-TE]
6-31 Unassigned (Standards Action)
OSPF Router Informational Capabilities Bits
Lindem, et al. Standards Track PAGE 6
RFC 4970 OSPF Capability Extensions July 2007
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
S1 and S2 bits in the LSA type determine the flooding scope. If AS-
wide flooding scope is chosen, the originating router should also
advertise area-scoped LSA(s) into any attached Not-So-Stubby Area
(NSSA) area(s). An OSPF router MAY advertise different capabilities
when both NSSA area scoped LSA(s) and an AS-scoped LSA are
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.
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 will need to be applied 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.
4. Security Considerations
This document describes both a generic mechanism for advertising
router capabilities and a TLV for advertising informational
capability bits. The latter TLV is less critical than the topology
information currently advertised by the base OSPF protocol. The
security considerations for the generic mechanism are dependent on
the future application and, as such, should be described as
additional capabilities are proposed for advertisement. Security
considerations for the base OSPF protocol are covered in [OSPF] and
[OSPFV3].
Lindem, et al. Standards Track PAGE 7
RFC 4970 OSPF Capability Extensions July 2007
5. IANA Considerations
The following IANA assignment was made from an existing registry:
The OSPFv2 opaque LSA type 4 has been reserved for the OSPFv2 RI
opaque LSA.
The following registries have been defined for the following
purposes:
1. Registry for OSPFv3 LSA Function Codes - This new top-level
registry will be comprised of the fields Value, LSA function code
name, and Document Reference. The OSPFv3 LSA function code is
defined in section A.4.2.1 of [OSPFV3]. The OSPFv3 LSA function
code 12 has been reserved for the OSPFv3 Router Information (RI)
LSA.
+-----------+-------------------------------------+
| Range | Assignment Policy |
+-----------+-------------------------------------+
| 0 | Reserved (not to be assigned) |
| | |
| 1-9 | Already assigned |
| | |
| 10-11 | Unassigned (Standards Action) |
| | |
| 12 | OSPFv3 RI LSA (Assigned herein) |
| | |
| 13-255 | Unassigned (Standards Action) |
| | |
| 256-8175 | Reserved (No assignments) |
| | |
| 8176-8183 | Experimentation (No assignments) |
| | |
| 8184-8191 | Vendor Private Use (No assignments) |
+-----------+-------------------------------------+
OSPFv3 LSA Function Codes
* OSPFv3 LSA function codes in the range 256-8175 are not to be
assigned at this time. Before any assignments can be made in
this range, there MUST be a Standards Track RFC that specifies
IANA Considerations that cover the range being assigned.
* OSPFv3 LSA function codes in the range 8176-8181 are for
experimental use; these will not be registered with IANA and
MUST NOT be mentioned by RFCs.
Lindem, et al. Standards Track PAGE 8
RFC 4970 OSPF Capability Extensions July 2007
* OSPFv3 LSAs with an LSA Function Code in the Vendor Private
Use range 8184-8191 MUST include the Vendor Enterprise Code as
the first 4 octets following the 20 octets of LSA header.
* If a new LSA Function Code is documented, the documentation
MUST include the valid combinations of the U, S2, and S1 bits
for the LSA. It SHOULD also describe how the Link State ID is
to be assigned.
2. Registry for OSPF RI TLVs - This top-level registry will be
comprised of the fields Value, TLV Name, and Document Reference.
The value of 1 for the capabilities TLV is defined herein.
+-------------+-----------------------------------+
| Range | Assignment Policy |
+-------------+-----------------------------------+
| 0 | Reserved (not to be assigned) |
| | |
| 1 | Already assigned |
| | |
| 2-32767 | Unassigned (Standards Action) |
| | |
| 32768-32777 | Experimentation (No assignements) |
| | |
| 32778-65535 | Reserved (Not to be assigned) |
+-----------+-------------------------------------+
OSPF RI TLVs
* Types in the range 32768-32777 are for experimental use; these
will not be registered with IANA and MUST NOT be mentioned by
RFCs.
* Types in the range 32778-65535 are reserved and are not to be
assigned at this time. Before any assignments can be made in
this range, there MUST be a Standards Track RFC that specifies
IANA Considerations that covers the range being assigned.
3. Registry for OSPF Router Informational Capability Bits - This
sub-registry of the OSPF RI TLV registry will be comprised of the
fields Bit Number, Capability Name, and Document Reference. The
values are defined in Section 2.4. All Router Informational
Capability TLV additions are to be assigned through standards
action.
Lindem, et al. Standards Track PAGE 9
RFC 4970 OSPF Capability Extensions July 2007
6. References
6.1. Normative References
[OPAQUE] Coltun, R., "The OSPF Opaque LSA Option", RFC 2370,
July 1998.
[OSPF] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
April 1998.
[OSPFV3] Coltun, R., Ferguson, D., and J. Moy, "OSPF for
IPv6", RFC 2740, December 1999.
[RFC-KEYWORDS] Bradner, S., "Key words for use in RFC's to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[TE] Katz, D., Kompella, K., and D. Yeung, "Traffic
Engineering Extensions to OSPF", RFC 3630,
September 2003.
6.2. Informative References
[EXP-TE] Srisuresh, P. and P. Joseph, "OSPF-xTE: Experimental
Extension to OSPF for Traffic Engineering", RFC 4973,
July 2007.
[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", Work
in Progress, April 2006.
[STUB] Retana, A., Nguyen, L., White, R., Zinin, A., and D.
McPherson, "OSPF Stub Router Advertisement",
RFC 3137, June 2001.
Lindem, et al. Standards Track PAGE 10
RFC 4970 OSPF Capability Extensions July 2007
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 document.
Comments from Abhay Roy, Vishwas Manral, Vivek Dubey, and Adrian
Farrel have been incorporated into later versions.
The RFC text was produced using Marshall Rose's xml2rfc tool.
Lindem, et al. Standards Track PAGE 11
RFC 4970 OSPF Capability Extensions July 2007
Authors' Addresses
Acee Lindem (editor)
Redback Networks
102 Carric Bend Court
Cary, NC 27519
USA
EMail: acee@redback.com
Naiming Shen
Cisco Systems
225 West Tasman Drive
San Jose, CA 95134
USA
EMail: naiming@cisco.com
Jean-Philippe Vasseur
Cisco Systems
1414 Massachusetts Avenue
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: sshaffer@bridgeport-networks.com
Lindem, et al. Standards Track PAGE 12
RFC 4970 OSPF Capability Extensions July 2007
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Copyright © The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
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Acknowledgement
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Internet Society.
Lindem, et al. Standards Track PAGE 13
Extensions to OSPF for Advertising Optional Router Capabilities
RFC TOTAL SIZE: 26416 bytes
PUBLICATION DATE: Wednesday, July 18th, 2007
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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