Network Working Group N. Shen
Request for Comments: 2763 Siara Systems
Category: Informational H. Smit
Dynamic Hostname Exchange Mechanism
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 (C) The Internet Society (2000). All Rights Reserved.
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.
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.
Shen & Smit Informational [Page 1]RFC 2763 Dynamic Hostname February 2000
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
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
Shen & Smit Informational [Page 2]RFC 2763 Dynamic Hostname February 2000