IS-IS Working Group Christian Martin
Verizon
IETF Internet Draft Stefano Previdi
Cisco Systems
Brad Neal
Broadwing Communications
Expires: August 2005 February 2005
A Policy Control Mechanism in IS-IS Using Administrative Tags
<draft-ietf-isis-admin-tags-03.txt>
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Martin, Previdi, Neal. [Page 1]
Internet Draft draft-ietf-isis-admin-tags-03.txt February 2005
Abstract
This document describes an extension to the IS-IS protocol to add
operational capabilities that allow for ease of management and
control over IP prefix distribution within an IS-IS domain. This
document enhances the IS-IS protocol by extending the information
that a Intermediate System (IS) [router] can place in Link State
Protocol Data Units (LSPs) for policy use. This extension will
provide operators with a mechanism to control IP prefix distribution
throughout multi-level IS-IS domains. Additionally, the information
can be placed in LSPs that have TLVs as yet undefined, if this
information is used to convey the same meaning in these future TLVs
as it is used in the currently defined TLVs.
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.
1. Introduction
As defined in [2] and extended in [3], the IS-IS protocol may be used
to distribute IPv4 prefix reachability information throughout an IS-
IS domain. In addition, thanks to extensions made in [6] and [7], IS-
IS may be used to distribute IPv6 reachability information.
The IPv4 prefix information is encoded as TLV type 128 and 130 in
[2], with additional information carried in TLV 135 as specified in
[3] and TLV 235 as defined in [6]. In particular, the extended IP
Reachability TLV (TLV 135) contains support for a larger metric
space, an up/down bit to indicate redistribution between different
levels in the hierarchy, an IP prefix, and one or more sub-TLVs that
can be used to carry specific information about the prefix. TLV 235
is a derivative of TLV 135, with the addition of Multi-Topology
membership information [6]. The IPv6 prefix information is encoded as
TLV 236 in [7] and TLV 237 in [6].
As of this writing no sub-TLVs have been defined; however, this draft
proposes 2 new sub-TLVs for TLV 135, TLV 235, TLV 236 and TLV 237
that may be used to carry administrative information about an IP
prefix.
Martin, Previdi, Neal. [Page 2]
Internet Draft draft-ietf-isis-admin-tags-03.txt February 2005
2. Sub-TLV Additions
This draft proposes 2 new "Administrative Tag" sub-TLVs to be added
to TLV 135, TLV 235, TLV 236 and TLV 237. These TLVs specify one or
more ordered, 32 or 64 bit unsigned integers that may be associated
with an IP prefix. Example uses of these tags include controlling
redistribution between levels and areas, different routing protocols,
or multiple instances of IS-IS running on the same router, or
carrying BGP standard or extended communities.
The methods for which their use is employed is beyond the scope of
this document and left to the implementer and/or operator.
The encoding of the sub-TLV(s) is discussed in the following
subsections.
2.1. 32-bit Administrative Tag Sub-TLV 1
The Administrative Tag SHALL be encoded as one or more 4 octet
unsigned integers using Sub-TLV 1 in TLV-135 [3], TLV 235 [6], TLV
236 [7] and TLV 237 [6]. The Administrative Tag Sub-TLV has following
structure:
1 octet of type (value: 1)
1 octet of length (value: multiple of 4)
one or more instances of 4 octets of administrative tag
An implementation MAY consider only one of the encoded tags, in which
case the first encoded tag MUST be considered. A tag value of zero
is reserved and SHOULD be treated as "no tag".
2.2. 64-bit Administrative Tag Sub-TLV 2
The Administrative Tag SHALL be encoded as one or more 8 octet
unsigned integers using Sub-TLV 2 in TLV-135 [3], TLV 235 [6], TLV
236 [7] and TLV 237 [6]. The 64-bit Administrative Tag Sub-TLV has
following structure:
1 octet of type (value: 2)
1 octet of length (value: multiple of 8)
one or more instances of 8 octets of administrative tag
Martin, Previdi, Neal. [Page 3]
Internet Draft draft-ietf-isis-admin-tags-03.txt February 2005
An implementation MAY consider only one of the encoded tags, in which
case the first encoded tag MUST be considered. A tag value of zero
is reserved and SHOULD be treated as "no tag".
3. Ordering of Tags
The semantics of the tag order are implementation-dependent. That
is, there is no implied meaning to the ordering of the tags that
indicates a certain operation or set of operations need be performed
based on the order of the tags. Each tag SHOULD be treated as an
autonomous identifier that MAY be used in policy to perform a policy
action. Whether or not tag A precedes or succeeds tag B SHOULD not
change the meaning of the tag set. However, an implementation MAY
wish to preserve tag ordering such that an ordered set of tags has
meaning to the local policy.
Each IS that receives an LSP with TLV(s) 135 and/or 235 and/or 236
and/or 237, that have associated SubTLV(s) 1 and/or 2, MAY operate on
the tag values as warranted by the implementation. If an
implementation needs to change tag values, for example, at an area
boundary, then the TLV(s) SHOULD be copied to the newly generated
Level-1 or Level-2 LSP at which point, the contents of the SubTLV(s)
MAY change as dictated by the policy action. In the event that no
change is required, the SubTLV(s) SHOULD be copied in order into the
new LSP, such that ordering is preserved.
4. Compliance
A compliant IS-IS implementation MUST be able to assign one tag to
any IP prefix in any of the following TLVs: TLV 135, TLV 235, TLV
236, TLV 237.
A compliant IS-IS implementation MAY be able to assign more than one
tag to any IP prefix in any of the following TLVs: TLV 135, TLV 235,
TLV 236, TLV 237.
A compliant IS-IS implementation MAY be able to rewrite or remove one
or more tags associated with a prefix in any of the following TLVs:
TLV 135, TLV 235, TLV 236, TLV 237.
5. Operations
An administrator associates an Administrative Tag value with some
interesting property. When IS-IS advertises reachability for some IP
Martin, Previdi, Neal. [Page 4]
Internet Draft draft-ietf-isis-admin-tags-03.txt February 2005
prefix that has that property, it adds the Administrative Tag to the
IP reachability information TLV for that prefix, and the tag "sticks"
to the prefix as it is flooded throughout the routing domain.
Consider the network in figure 1. We wish to "leak" L1 prefixes [5]
with some property, A, from L2 to the L1 router R1. Without policy-
groups, there is no way for R2 to know property A prefixes from
property B prefixes.
R2--------R3--------R4
L2 / \
- - - /- - - - - - - - - - - - - -
L1 / \
R1----1.1.1.0/24 (A) R5
|
|
1.1.2.0/24 (B)
Figure 1
We associate Administrative Tag 100 with property A, and have R5
attach that value to the IP extended reachability information TLV for
prefix 1.1.2.0/24. R2 has a policy in place to "match prefixes with
Administrative Tag 100, and leak to L1."
The previous example is rather simplistic; it seems that it would be
just as easy for R2 simply to match the prefix 1.1.2.0/24. However,
if there are a large number of routers that need to apply some policy
according to property A and large number of "A" prefixes, this
mechanism can be quite helpful.
6. Security Considerations
This document raises no new security issues for IS-IS, as any
annotations to IP prefixes should not pass outside the administrative
control of the network operator of the IS-IS domain. Such an
allowance would violate the spirit of Interior Gateway Protocols in
general and IS-IS in particular
Martin, Previdi, Neal. [Page 5]
Internet Draft draft-ietf-isis-admin-tags-03.txt February 2005
7. IANA Considerations
The authors have chosen "1" as the type code of the 32-bits
Administrative Tag Sub-TLV and "2" as the type code of the 64-bits
Administrative Tag Sub-TLV. These values must be allocated by IANA.
8. Intellectual Property Statement
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..
8.1. IPR Disclosure Acknowledgement
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with
RFC 3668.
9. Acknowledgments
The authors would like to thank Henk Smit for clarifying the best
place to describe this new information, Tony Li and Tony Przygienda
for useful comments on this draft, Danny McPherson for some much
needed formatting assistance, and Mike Shand for useful discussions
on encoding structure of the sub-TLV.
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Internet Draft draft-ietf-isis-admin-tags-03.txt February 2005
10. References
10.1. Normative references
[RFC] Bradner, S., "Key words for use in RFCs to indicate
requirements levels", RFC 2119, March 1997.
[RFC3667] Bradner, S., "IETF Rights in Contributions", BCP 78,
RFC 3667, February 2004.
[RFC3668] Bradner, S., Ed., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3668, February 2004.
[1] "Intermediate System to Intermediate System Intra-Domain Routing
Exchange Protocol " ISO 10589.
[2] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual
environments", RFC 1195, December 1990.
[3] Li, T., Smit, H., "IS-IS extensions for Traffic Engineering", RFC
3784, June 2004.
[4] Adwuche, D., Malcolm, J., Agogbua, M., O'Dell, M. and McManus,
J., "Requirements for Traffic Engineering Over MPLS," RFC 2702,
September 1999.
[5] Li,T., Przygienda, T., Smit, H., "Domain-wide Prefix Distribution
with Two-Level IS-IS" RFC 2966, October 2000
10.2. Informative References
[6] Przygienda, T., Shen, N., Sheth, N., "M-ISIS: Multi Topology
Routing in IS-IS", draft-ietf-isis-wg-multi-topology-03.txt, April
2002.
[7] Hopps, C., "Routing IPv6 with IS-IS", draft-ietf-isis-ipv6-
05.txt, January 2003
11. Editors' Address
Christian Martin
Verizon
1880 Campus Commons Dr
Reston, VA 20191
Email: cmartin@verizon.com
Martin, Previdi, Neal. [Page 7]
Internet Draft draft-ietf-isis-admin-tags-03.txt February 2005
Stefano Previdi
Cisco Systems, Inc.
Via Del Serafico, 200
00142 Roma - Italy
email: sprevidi@cisco.com
Brad Neal
Broadwing Communications
1835 Kramer Lane - Suite 100
Austin, TX 78758
USA
Email: bneal@broadwing.com
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Martin, Previdi, Neal. [Page 8]
