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Versions: (draft-vasseur-isis-caps) 00 01 02
03 04 05 06 07 RFC 4971
Network Working Group Jean-Philippe Vasseur(Ed)
Internet Draft Naiming Shen (Ed)
Proposed status: Standard Cisco Systems, Inc.
Expires: August 2007 Rahul Aggarwal(Ed)
Juniper Networks
February 2007
IS-IS Extensions for Advertising Router Information
draft-ietf-isis-caps-07.txt
Status of this Memo
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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.
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 [RFC-2119].
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Table of Contents
1. Introduction...................................................2
2. IS-IS Router CAPABILITY TLV....................................3
3. Element of procedure...........................................3
4. Interoperability with routers not supporting the capability TLV.5
5. Security considerations........................................5
6. Acknowledgment.................................................6
7. Intellectual Property Considerations...........................6
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
[IS-IS, IS-IS-IP] routers to learn the capabilities of the other
routers of their IS-IS level, area or routing domain. 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 [IS-IS-TE]
requires some significant configuration effort. [AUTOMESH]
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 ([TE-
NODE-CAP]) allows an LSR to advertise its Point To Multipoint
capabilities ([P2MP] and [P2MP-REQS]).
3. Inter-area traffic engineering: Advertisement of the IPv4
and/or the IPv6 Traffic Engineering Router IDs.
The use of IS-IS 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
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.
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2. IS-IS Router CAPABILITY TLV
The IS-IS Router CAPABILITY TLV is composed of 1 octet for the type,
1 octet specifying the number of bytes in the value field, 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. Sub-TLVs are
formatted as described in RFC 3784 [IS-IS-TE].
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.
3. Elements of procedure
A router which generates a CAPABILITY TLV MUST have a Router ID
which is a 32 bit number. The ID MUST be unique within the IS-IS
area. If the router generates any capability TLVs with domain
flooding scope then the ID MUST also be unique within the IS-IS
routing domain.
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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
will 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 will 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 will be leaked
into other IS-IS levels. When the TLV is leaked from level-2 to
level-1, the D bit will be set in the level-1 LSP advertisement.
In order to prevent the use of stale capabilities information 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.
Example: If Level-1 router A generates a Capability TLV and floods
it to two L1/L2 routers S and T, they will flood it into the Level-2
domain. Now suppose the Level-1 area partitions, such that A and S
are in one partition and T is in another. IP routing will still
continue to work, but if A now issues a revised version of the CAP
TLV, or decides to stop advertising it, S will follow suit, but T
will continue to advertise the old version until the LSP times out.
Routers in other areas have to choose whether to trust T's copy of
A's capabilities or S's copy of A's information and they have no
reliable way to choose. By making sure that T stops leaking A's
information, this removes the possibility that other routers will
use stale information from A.
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
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capabilities TLV in the same LSP fragment as the advertisement which
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
Any new security issues raised by the procedures in this document
depend upon the opportunity for LSPs to be snooped and modified,
the ease/difficulty of which has not been altered. As the LSPs may
now contain additional information regarding router capabilities,
this new information would also become available to an attacker.
Specifications based on this mechanism need to describe the
security considerations around the disclosure and modification
of their information. Note that an integrity mechanism, such as
one defined in RFC3567 or draft-ietf-isis-hmac-sha, should be
applied if there is high risk resulting from modification of
capability information.
6. IANA considerations
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IANA will assign a new IS-IS TLV code-point for the newly defined IS-
IS TLV type named the IS-IS Router CAPABILITY TLV and defined in this
document. Suggested value is 242 (to be assigned by IANA).
7. Acknowledgment
The authors would like to thank Jean-Louis Le Roux, Paul Mabey,
Andrew Partan and Adrian Farrel for their useful comments.
8. 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
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.
9. References
9.1 Normative references
[RFC-2119] 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.
[IS-IS-TE] Li, T., Smit, H., "IS-IS extensions for Traffic
Engineering", RFC 3784, June 2004.
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9.2 Informative references
[AUTOMESH] JP Vasseur, JL. Le Roux et al, "Routing extensions for
discovery of Multiprotocol (MPLS) Label Switch Router (LSR) Traffic
Engineering (TE) mesh membership", draft-ietf-ccamp-automesh, work in
progress.
[TE-NODE-CAP] JP Vasseur, JL. Le Roux et al, "Routing extensions for
discovery of Traffic Engineering Node Capabilities", draft-ietf-
ccamp-te-node-cap, 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, work in progress.
[P2MP-REQS] S. Yasukawa et al. "Requirements for point to multipoint
extension to RSVP", draft-ietf-mpls-p2mp-sig-requirement, work in
progress.
10. Authors' Addresses
Jean-Philippe Vasseur
CISCO Systems, Inc.
1414 Massachusetts Avenue
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
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draft-ietf-isis-caps-07.txt February 2007
Acee Lindem
Redback Networks
102 Carric Bend Court
Cary, NC 27519
USA
e-mail: acee@redback.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
e-mail: rahul@juniper.net
Scott Shaffer
e-mail: sshaffer@bridgeport-networks.com
Full Copyright Statement
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Vasseur et al. [Page 8]
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