Network Working Group Acee Lindem (Redback Networks)
Internet Draft Naiming Shen (Redback Networks)
Expiration Date: November 2003 Rahul Aggarwal (Redback Networks)
Scott Shaffer (Genuity, Inc.)
JP Vasseur (Cisco Systems, Inc)
Extensions to OSPF for Advertising Optional Router Capabilities
draft-lindem-ospf-cap-00.txt
Status of this Memo
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Abstract
It is useful for routers in an OSPF routing domain to know the
capabilities of their neighbors and other routers in the OSPF
routing domain. This draft proposes extensions to OSPF for
advertising optional router capabilities. A new Router
Information opaque LSA is proposed for this purpose.
Conventions used in this document
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 [3].
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Internet Draft draft-lindem-ospf-cap-00.txt May 2003
1. Motivation
It is useful for routers in an OSPF routing domain to know the
capabilities of their neighbors and other routers in the OSPF
routing domain. This can be useful for various applications:
o In MPLS Traffic Engineering (TE), it can be used as a discovery
mechanism [7, 8] to announce a LSR's TE capabilities like
Path Computation Server capability (Capability of a LSR to be
a Path Computation Server for TE LSP path computation) or the
intention of a LSR to be part of a particular MPLS TE mesh group.
o For network management and troubleshooting. It gives operators a
network wide view of OSPF capabilities on different routers.
The presence of a capability on a given router implies
that the software version supports the capability and the router
is configured to support it. On the other hand, the absence of an
expected capability on a particular router can imply either
misconfiguration or an incorrect software version. Hence, this
capability information can be used to track problems resulting from
misconfiguration or an incorrect software version.
OSPF uses the options field in the hello packet to advertise optional
router capabilities [1]. However, all the bits in this field have
been allocated and there is no way to advertise new optional
or MPLS TE capabilities. This document proposes extensions to OSPF
to advertise these optional capabilities. For existing OSPF
capabilities, this advertisement will be used primarily for
informational purposes. For MPLS TE features, it is used for
advertisement and discovery. Future OSPF features could also
use this mechanism for advertisement and discovery.
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2. OSPF Router Information LSA
OSPF routers will optionally advertise their optional capabilities
in an area-scoped, local scope, or AS-scoped Opaque-LSA [2].
If a router does not advertise this LSA, it does not imply that the
router does not support one or more of the defined capabilities.
For existing OSPF capabilities, this advertisement will be used
primarily for informational purposes. For MPLS TE features,
it is used for advertisement and discovery. Future OSPF features
could also use this mechanism for advertisement and discovery.
For current OSPF capabilities, the advertisement will be used for
The Router Information opaque LSA will be originated at startup and
reoriginated when router capabilities change or when the LSA is
periodically refreshed.
The Router Information LSA will have 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 -+
| ... |
Figure 2. OSPF Router Information LSA
The format of the TLVs within the body of a Router Information LSA is
the same as the TLV format used by the Traffic Engineering Extensions
to OSPF [3]. The TLV header consists of a 16-bit Type field and a
16-bit length field, and is followed by zero or more bytes of value.
The length field indicates the length of the value portion in bytes.
The value portion is padded to four-octet alignment, but the padding
is not included in the length field. For example, a one byte value
would have the length field set to 1, and three bytes of padding
would be added to the end of the value portion of the TLV.
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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... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3. OSPF TLV Format
2.1 OSPF Router Capability TLV
The first TLV in the body of a Router Information LSA is the
Router Capability TLV. It MUST be included. A router advertising
an optional Router Information LSA SHOULD set the supported optional
capabilities, unless they are explicitly configured off, in the
Router Capability TLV.
The format of the Router Capability 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router Capability sub-TLV | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional sub-TLVs |
Figure 4. OSPF Router Capability TLV
Type A 16 bit field set to 1.
Length A 16 bit field that indicates the length of the TLV,
other than the Type and the Length fields in bytes.
The first four bytes of the TLV are reserved. This is followed by
a Router Capability sub-TLV that MUST be included. The format of
the Router Capability sub-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5. OSPF Router Capability Sub-TLV
Type A 16 bit field set to 1.
Length A 16 bit field that indicates the length of the value
portion in bytes. Its set to N x 4 octets. N starts from
1 and can be increased when there is a need. Each 4
octets are referred to as a capability flag.
Value This comprises one or more capability flags. For each 4
octets, the bits are indexed from the most significant
to the least significant, where each bit represents one
router capability. When the first 32 capabilities are
defined, a new capability flag will be used to
accommodate the next capability.
The Router Capability sub-TLV MAY be followed by optional sub-TLVs.
In some cases it may be desirable to advertise additional information
for a particular capability. This can be done by including other
sub-TLVs.
2.2 Reserved OSPF Router Capability Bits
We have assigned some pre-determined bits to the first capability
flag.
Bit Capabilities
0-3 Reserved
4 OSPF graceful restart capable [5]
5 OSPF graceful restart helper [5]
6 Stub Router support [6]
7 Traffic Engineering support [4]
8 OSPF point-to-point over LAN [9]
9 OSPF Path Computation Server discovery [7, 8]
10-31 Future assignments
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2.3 Flooding Scope of the Router Information LSA
The flooding scope of the Router Information opaque LSA is determined
by the LSA type. A type 10 (area-scoped) opaque LSA or a type 11
(AS-scoped) LSA may be used. The choice of flooding scope is made
by the advertising router and is a matter of local policy. A Router
Information LSA must be announced using only one flooding scope.
3. Security Consideration
This memo does not create any new security issues for the OSPF
protocol. Security considerations for the base OSPF protocol are
covered in [1].
4. Acknowledgments
The idea for this work grew out of a conversation with Andrew Partan
and we would like to thank him for his contribution.
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5. IANA Considerations
A new opaque LSA type will need to be assigned by IANA. Additionally,
IANA will need to have registries for the Router Information opaque
LSA TLVs. The TLV assignee will be responsible for allocation of
any sub-TLVs for the IANA assigned TLV. All TLVs and sub-TLVs will
be subject to OSPF WG review.
6. References
Normative References
[1] Coltun, R., "The OSPF Opaque LSA Option", RFC 2370, July
1998.
[2] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Level", BCP 14, RFC 2119, March 1997.
Informative References
[4] Katz, D., D. Yeung and K. Kompella, "Traffic Engineering
Extensions to OSPF", Internet Draft, work in progress.
[5] Moy, J., "OSPF Graceful OSPF Restart", Internet Draft, work in
progress.
[6] Retana, A., et al, "OSPF Stub Router Advertisement",
RFC 3137, June 2001.
[7] Vasseur, Psenak, "Traffic Engineering Capability TLV for OSPF",
Internet Draft, work in progress.
[8] Vasseur et al, "RSVP Path computation request and reply
messages", draft-vasseur-mpls-computation-rsvp-te-03.txt,
work in progress
[9] N. Shen, et al, "Point-to-point operation over LAN in
link-state-routing protocols", Internet Draft, work in
progress.
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9. Author Information
Acee Lindem
Redback Networks
350 Holger Way
San Jose, CA 95134
e-mail: acee@redback.com
Naiming Shen
Redback Networks
350 Holger Way
San Jose, CA 95134
e-mail: naiming@redback.com
Rahul Aggarwal
Redback Networks
350 Holger Way
San Jose, CA 95134
e-mail: rahul@redback.com
Scott Shaffer
Genuity, Inc.
3 Van de Graaff Drive
PO Box 3073
Burlington, MA 01803
e-mail: sshaffer@genuity.com
JP Vasseur
Cisco Systems, Inc.
300 Apollo Drive
Chelmsford, MA 01824
e-mail: jpv@cisco.com
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