draft-ietf-isis-caps-00.txt January 2005
ISIS WG
Internet Draft Jean-Philippe Vasseur(Ed)
Cisco Systems, Inc.
Rahul Aggarwal(Ed)
Juniper Networks
Naiming Shen(Ed)
Redback Networks
Expires: July 2005 January 2005
IS-IS extensions for advertising router information
draft-ietf-isis-caps-00.txt
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Abstract
This document defines a new optional IS-IS TLV named CAPABILITY,
formed of multiple sub-TLVs, which allows a router to announce its
capabilities within an IS-IS level or the entire routing domain.
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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 [ii].
Table of Contents
1. Introduction............................................2
2. IS-IS Router CAPABILITY TLV.............................3
3. Element of procedure....................................4
4. Interoperability with routers not supporting the
capability TLV..........................................5
5. Security considerations.................................5
6. Acknowledgment..........................................5
7. Intellectual Property Considerations....................5
8. References..............................................6
Normative references.......................................6
Informative references.....................................6
9. Author's Addresses......................................7
1. Introduction
There are several situations where it is useful for the IS-IS
routers to learn the capabilities of the other routers of their IS-
IS level, area or routing domain. Some applications are described
in [IS-IS-TE-CAP]. For the sake of illustration, two examples
related to MPLS Traffic Engineering are described here:
1. Mesh-group: the setting up of a mesh of TE LSPs requires some
significant configuration effort. [IS-IS-TE-CAP] proposes an auto-
discovery mechanism whereby every LSR of a mesh advertises its
mesh-group membership by means of IS-IS extensions.
2. Point to Multi-point TE LSP (P2MP LSP). A specific sub-TLV ([IS-
IS-TE]) allows an LSR to advertise its Point To Multipoint
capabilities ([P2MP] and [P2MP-REQS]).
The use of ISIS for Path Computation Element (PCE) discovery may also
be considered and will be discussed in the PCE WG.
The capabilities mentioned above require the specification of new
sub-TLVs carried within the CAPABILITY TLV defined in this document.
Note that the examples above are provided for the sake of
illustration. This document proposes a generic capability advertising
mechanism not limited to MPLS Traffic Engineering.
This document defines a new optional IS-IS TLV named CAPABILITY,
formed of multiple sub-TLVs, which allows a router to announce its
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capabilities within an IS-IS level or the entire routing domain. The
applications mentioned above require the specification of new sub-
TLVs carried within the CAPABILITY TLV defined in this document.
Definition of these sub-TLVs is outside the scope of this document.
2. IS-IS Router CAPABILITY TLV
The IS-IS Router CAPABILITY TLV is composed of 1 octet for the type,
1 octet specifying the TLV length, 1 octet of bit flags and a
variable length value field, starting with 4 octets of Router ID,
indicating the source of the TLV, and followed by 1 octet of flags. A
set of optional sub-TLVs may follow the flag field.
TYPE: 242 (To be assigned by IANA)
LENGTH: from 5 to 255
VALUE:
Router ID (4 octets)
Flags (1 octet)
Set of optional sub-TLVs (0-250 octets)
Flags
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Reserved |D|S|
+-+-+-+-+-+-+-+-+
Currently two bit flags are defined.
S bit (0x01): If the S bit is set(1), the IS-IS Router CAPABILITY TLV
MUST be flooded across the entire routing domain. If the S bit is not
set(0), the TLV MUST NOT be leaked between levels. This bit MUST NOT
be altered during the TLV leaking.
D bit (0x02): When the IS-IS Router CAPABILITY TLV is leaked from
level-2 to level-1, the D bit MUST be set. Otherwise this bit MUST be
clear. IS-IS Router capability TLVs with the D bit set MUST NOT be
leaked from level-1 to level-2. This is to prevent TLV looping.
The Router CAPABILITY TLV is OPTIONAL. As specified in section 3,
more than one Router CAPABILITY TLVs from the same source MAY be
present.
This document does not specify how an application may use the Router
Capability TLV and such specification is outside the scope of this
document.
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3. Elements of procedure
When advertising capabilities with different flooding scopes, a
router MUST originate a minimum of two Router CAPABILITY TLVs, each
TLV carrying the set of sub-TLVs with the same flooding scope. For
instance, if a router advertises two sets of capabilities C1 and C2
with an area/level scope and routing domain scope respectively, C1
and C2 being specified by their respective sub-TLV(s), the router
MUST originate two Router CAPABILITY TLVs:
- One Router CAPABILITY TLV with the S flag cleared, carrying the
sub-TLV(s) relative to C1. This Router CAPABILITY TLV MUST NOT be
leaked into another level.
- One Router CAPABILITY TLV with the S flag set, carrying the sub-
TLV(s) relative to C2. This Router CAPABILITY TLV MUST be leaked
into other IS-IS levels. When the TLV is leaked from level-2 to
level-1, the D bit MUST be set in the level-1 LSP advertisement.
When leaking Capability TLVs downward from Level-2 into Level-1, if
the originator of the TLV is a Level-1 router in another area, it is
possible that multiple copies of the same TLV may be received from
multiple L2 routers in the originating area. To prevent a router from
leaking multiple copies of the same TLV, the router performing the
downward leaking MUST check for such duplication by comparing the
contents of the TLVs.
A system MUST NOT use a Capability TLV present in an LSP of a system
which is not currently reachable via Level-x paths, where "x" is the
level (1 or 2) in which the sending system advertised the TLV. This
requirement applies regardless of whether the sending system is the
originator of the Capabilities TLV or not. Note that leaking a
Capabilities TLV is one of the uses which is prohibited under these
conditions.
In IS-IS, the atomic unit of the update process is a TLV - or more
precisely in the case of TLVs which allow multiple entries to appear
in the value field (e.g. IS-neighbors) - an entry in the value field
of a TLV. If an update to an entry in a TLV is advertised in an LSP
fragment different from the LSP fragment associated with the old
advertisement, the possibility exists that other systems can
temporarily have either 0 copies of a particular advertisement or 2
copies of a particular advertisement, depending on the order in which
new copies of the LSP fragment which had the old advertisement and
the fragment which has the new advertisement arrive at other systems.
Wherever possible, an implementation SHOULD advertise the update to a
capabilities TLV in the same LSP fragment as the advertisement which
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it replaces. Where this is not possible, the two affected LSP
fragments should be flooded as an atomic action.
Systems which receive an update to an existing capability TLV can
minimize the potential disruption associated with the update by
employing a holddown time prior to processing the update so as to
allow for the receipt of multiple LSP fragments associated with the
same update prior to beginning processing.
Where a receiving system has two copies of a capabilities TLV from
the same system which have different settings for a given attribute,
the procedure used to choose which copy shall be used is undefined.
4. Interoperability with routers not supporting the capability TLV.
Routers which do not support the Router CAPABILITY TLV MUST silently
ignore the TLV(s) and continue processing other TLVs in the same LSP.
Routers which do not support specific sub-TLVs carried within a
Router CAPABILITY TLV MUST silently ignore the unsupported sub-TLVs
and continue processing those sub-TLVs in the Router CAPABILITY TLV
which are supported. How partial support may impact the operation of
the capabilities advertised within the Router CAPABILITY TLV is
outside the scope of this document.
In order for Router CAPABILITY TLVs with domain-wide scope originated
by L1 Routers to be flooded across the entire domain at least one
L1/L2 Router in every area of the domain MUST support the Router
CAPABILITY TLV.
If leaking of the CAP TLV is required, the entire CAP TLV MUST be
leaked into another level even though it may contain some of the
unsupported sub-TLVs.
5. Security considerations
No new security issues are raised in this document.
6. Acknowledgments
The authors would like to thank Jean-Louis Le Roux, Paul Mabey and
Andrew Partan for their useful comments.
7. Intellectual Property Considerations
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
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made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
8. References
Normative references
[RFC] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels," RFC 2119.
[IS-IS] "Intermediate System to Intermediate System Intra-Domain
Routeing Exchange Protocol for use in Conjunction with the Protocol
for Providing the Connectionless-mode Network Service (ISO 8473)",
ISO 10589.
[IS-IS-IP] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[ISIS-TE] Li, T., Smit, H., "IS-IS extensions for Traffic
Engineering", RFC 3784, June 2004.
Informative references
[IS-IS-TE-CAP] JP Vasseur, S. Previdi, Paul Mabey and JL. Le Roux,
ôIS-IS MPLS Traffic Engineering capabilitiesö, draft-vasseur-isis-te-
caps-00.txt, work in progress.
[P2MP] R. Aggarwal,D. Papadimitriou,S. Yasukawa, et. al. "Extensions
to RSVP-TE for Point To Multipoint TE LSPs", draft-ietf-mpls-rsvp-te-
p2mp-00.txt, work in progress.
[P2MP-REQS] S. Yasukawa et al. ½ Requirements for point to multipoint
extension to RSVP ©, draft-ietf-mpls-p2mp-sig-requirement-00.txt,
work in progress.
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9. Author's Addresses
Jean-Philippe Vasseur
CISCO Systems, Inc.
300 Beaver Brook
Boxborough, MA 01719
USA
Email: jpv@cisco.com
Stefano Previdi
CISCO Systems, Inc.
Via Del Serafico 200
00142 - Roma
ITALY
Email: sprevidi@cisco.com
Mike Shand
Cisco Systems
250 Longwater Avenue,
Reading,
Berkshire,
RG2 6GB
UK
Email: mshand@cisco.com
Les Ginsberg
Cisco Systems
510 McCarthy Blvd.
Milpitas, Ca. 95035 USA
Email: ginsberg@cisco.com
Acee Lindem
Cisco Systems
7025 Kit Creek Road
Research Triangle Park, NC 27709
USA
e-mail: acee@cisco.com
Naiming Shen
Cisco Systems
225 West Tasman Drive
San Jose, CA 95134
USA
e-mail: naiming@cisco.com
Rahul Aggarwal
Juniper Networks
1194 N. Mathilda Avenue
San Jose, CA 94089
USA
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e-mail: rahul@juniper.net
Scott Shaffer
e-mail: sshaffer@bridgeport-networks.com
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