Network Working Group Christian Martin
INTERNET DRAFT Verzion Global Networks, Inc.
Brad Neal
Broadwing Communications
Stefano Previdi
May 2002 Cisco Systems
A Policy Control Mechanism is IS-IS Using Administrative Tags
<draft-martin-neal-policy-isis-admin-tags-01.txt>
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
2. 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. The IS-
IS protocol is specified in [1], with extensions for supporting IPv4
specified in [2] and further enhancements for Traffic Engineering [4]
in [3].
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) as specified in [2]. This
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extension will provide operators with a mechanism to control IP
prefix distribution throughout multi-level IS-IS domains.
3. Specification of Requirements
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].
4. Introduction
As defined in [2] and extended in [3], the IS-IS protocol may be used
to distribute IP prefix reachibility information throughout an IS-IS
domain. The IP prefix information is encoded as TLV type 128 and 130
in [2],with additional information carried in TLV 135 as specified in
[3]. In particular, the extended IP Reachabilty 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.
As of this writing no sub-TLVs have been defined; however, this draft
proposes a new sub-TLV that may be used to carry administrative
information about an IP prefix.
5. Sub-TLV Additions
This draft proposes a new "Administrative Tag" sub-TLV to be added to
TLV 135. This TLV specifies one or more 32 bit unsigned integers
that may be associated with an IP prefix. Example uses of this tag
include controlling redistribution between levels and areas,
different routing protocols, or multiple instances of IS-IS running
on the same router.
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 is discussed in the following subsection.
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5.1. 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]. 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".
6. A compliant IS-IS implementation:
MUST be able to assign one tag to any IP prefix in TLV 135.
MAY be able to assign more than one tag to any IP prefix in TLV 135.
MAY be able to rewrite or remove one or more tags associated with a
prefix in TLV 135.
7. Operation
An administrator associates an Administrative Tag value with some
interesting property. When IS-IS advertises reachability for some IP
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 domian.
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 R5----1.1.1.0/24 (A)
|
|
1.1.2.0/24 (B)
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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 1.1.1.0/24. 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 1.1.1.0/24. 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.
8. 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.
9. IANA Considerations
The authors have chosen "1" as the value of the Administrative Tag
sub-TLV. This must be allocated by IANA.
10. Acknowledgments
The authors would like to thank Henk Smit for clarifying the best
place to describe this new information, Tony Li 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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11. References
[1] "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.
[2] Callon, R., RFC 1195, "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[3] Li, T., and Smit, H., "IS-IS extensions for Traffic Engineering",
Internet Draft, "Work in Progress", September 2000.
[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
12. Authors' Address
Christian Martin
Verizon Global Networks, Inc.
1880 Campus Commons Dr
Reston, VA 20191
USA
Email: cmartin@gnilink.net
Voice: 1 (703) 2954394
Fax: 1 (703) 2954279
Brad Neal
Broadwing Communications
1835 Kramer Lane - Suite 100
Austin, TX 78758
USA
Email: bneal@broadwing.com
Voice: 1 (512) 7421310
Fax: 1 (512) 7421333
Stefano Previdi
Cisco Systems, Inc.
De Kleetlaan 6A
1831 Diegem - Belgium
email: sprevidi@cisco.com
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