Network Working Group N. Shen
Request for Comments: 2763 Siara Systems
Category: Informational H. Smit
Cisco Systems
February 2000

Dynamic Hostname Exchange Mechanism
for IS-IS

Status of this Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2000). All Rights Reserved.

Abstract

Currently, there does not exist a simple and dynamic mechanism for
routers running IS-IS to learn about symbolic hostnames. This
document defines a new TLV which allows the IS-IS routers to flood
their name to system ID mapping information across the IS-IS network.

1. IntrodUCtion

IS-IS uses a 1-8 byte system ID (normally 6 bytes) to represent a
node in the network. For management and operation reasons, network
operators need to check the status of IS-IS adjacencies, entries in
the routing table and the content of the IS-IS link state database.
It is obvious that, when looking at diagnostics information,
hexadecimal representations of systemIDs and LSP identifiers are less
clear than symbolic names.

One way to overcome this problem is to define a name-to-systemID
mapping on a router. This mapping can be used bidirectionally. E.g.,
to find symbolic names for systemIDs, and to find systemIDs for
symbolic names. One way to build this table of mappings is by static
definitions. Among network administrators who use IS-IS as their IGP
it is current practice to define such static mappings.

Thus every router has to maintain a table with mappings between
router names and systemIDs. These tables need to contain all names
and systemIDs of all routers in the network.

There are several ways one could build such a table. One is via
static configurations. Another scheme that could be implemented is
via DNS lookups. In this document we propose a third solution. We
hope the proposed solution is easier and more manageable than static
mapping or DNS schemes.

2. Possible solutions

The obvious drawback of static configuration of mappings is the issue
of scalability and maintainability. The network operators have to
maintain the name tables. They have to maintain an entry in the table
for every router in the network. They have to maintain this table on
each router in the network. The effort to create and maintain these
static tables grows with the total number of routers on the network.
Changing the name or systemID of one router, or adding one new router
introduced will affect the configurations of all the other routers on
the network. This will make it very likely that those static tables
are outdated.

Having one table that can be updated in a centralized place would be
helpful. One could imagine using the DNS system for this. A drawback
is that during the time of network problems, the response time of DNS
services might not be satisfactory or the DNS services might not even
be available. Another possible drawback might be the added complexity
of DNS. Also, some DNS implementations might not support A and PTR
records for CLNS NSAPs.

A third way to build dynamic mappings would be to use the transport
mechanism of the routing protocol itself to advertise symbolic names
in IS-IS link-state PDU. This document defines a new TLV which allows
the IS-IS routers to include the name to systemID mapping information
in their LSPs. This will allow simple and reliable transport of name
mapping information across the IS-IS network.

3. The Dynamic Hostname TLV

The Dynamic hostname TLV is defined here as TLV type 137.

LENGTH - total length of the value field.

VALUE - a string of 1 to 255 bytes.

The Dynamic hostname TLV is optional. This TLV may be present in any
fragment of a non-pseudo node LSP. The value field identifies the
symbolic name of the router originating the LSP. This symbolic name
can be the FQDN for the router, it can be a subset of the FQDN or any
string operators want to use for the router. The use of FQDN or a

subset of it is strongly recommended. The content of this value is a
domain name, see RFC2181. The string is not null-terminated. The
systemID of this router can be derived from the LSP identifier.

If this TLV is present in a pseudo node LSP, then it should not be
interpreted as the DNS hostname of the router.

4. Implementation

The Dynamic Hostname TLV is optional. When originating an LSP, a
router may decide to include this TLV in its LSP. Upon receipt of an
LSP with the dynamic hostname TLV, a router may decide to ignore this
TLV, or to install the symbolic name and systemID in its hostname
mapping table.

A router may also optionally insert this TLV in it's pseudo node LSP
for the association of a symbolic name to a local LAN.

5. Security Considerations

This document raises no new security issues for IS-IS. However, it is
encouraged to use authentications for IS-IS routing protocol. The
authentication mechanism for IS-IS protocol is specified in [1] and
it is being enhanced within IETF in [2].

6. Acknowledgments

The authors would like to thank Enke Chen and Yakov Rekhter for their
comments on this work.

7. References

[1] ISO, "Intermediate system to Intermediate system routing
information exchange protocol for use in conjunction with the
Protocol for providing the Connectionless-mode Network Service
(ISO 8473)," ISO/IEC 10589:1992.

[2] Li, T., "IS-IS HMAC-MD5 Authentication", Work in Progress.

8. Authors' Addresses

Naiming Shen
Siara Systems, Inc.
1195 Borregas Avenue
Sunnyvale, CA, 94089

EMail: naiming@siara.com

Henk Smit
Cisco Systems, Inc.
170 Tasman Drive
San Jose, CA, 95134

EMail: hsmit@cisco.com

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