Configuring Iso Clns Routing - Cisco IE-4000 Software Configuration Manual

Configuring IP Unicast Routing

Configuring ISO CLNS Routing

Configuring ISO CLNS Routing
The International Organization for Standardization (ISO) Connectionless Network Service (CLNS) protocol is a standard
for the network layer of the Open System Interconnection (OSI) model. Addresses in the ISO network architecture are
referred to as network service access point (NSAP) addresses and network entity titles (NETs). Each node in an OSI
network has one or more NETs. In addition, each node has many NSAP addresses.
When you enable connectionless routing on the switch by using the clns routing global configuration command, the
switch makes only forwarding decisions, with no routing-related functionality. For dynamic routing, you must also enable
a routing protocol. The switch supports the Intermediate System-to-Intermediate System (IS-IS) dynamic routing
protocols for ISO CLNS networks. This routing protocol supports the concept of areas. Within an area, all routers know
how to reach all the system IDs. Between areas, routers know how to reach the proper area. IS-IS supports two levels
of routing: station routing (within an area) and area routing (between areas).
The key difference between the ISO IGRP and IS-IS NSAP addressing schemes is in the definition of area addresses.
Both use the system ID for Level 1 routing (routing within an area). However, they differ in the way addresses are specified
for area routing. An ISO IGRP NSAP address includes three separate fields for routing: the domain, area, and system ID.
An IS-IS address includes two fields: a single continuous area field (comprising the domain and area fields) and the
system ID.
For more detailed information about ISO CLNS, see the ISO CLNS documents listed in the
Configuring IS-IS Dynamic Routing
IS-IS is an ISO dynamic routing protocol. Enabling IS-IS requires that you create an IS-IS routing process and assign it
to a specific interface, rather than to a network. You can specify more than one IS-IS routing process per Layer 3 switch
or router by using the multiarea IS-IS configuration syntax. You then configure the parameters for each instance of the
IS-IS routing process.
Small IS-IS networks are built as a single area that includes all the routers in the network. As the network grows larger,
it is usually reorganized into a backbone area made up of the connected set of all Level 2 routers from all areas, which
is in turn connected to local areas. Within a local area, routers know how to reach all system IDs. Between areas, routers
know how to reach the backbone, and the backbone routers know how to reach other areas.
Routers establish Level 1 adjacencies to perform routing within a local area (station routing). Routers establish Level 2
adjacencies to perform routing between Level 1 areas (area routing).
A single Cisco router can participate in routing in up to 29 areas and can perform Level 2 routing in the backbone. In
general, each routing process corresponds to an area. By default, the first instance of the routing process configured
performs both Level 1and Level 2 routing. You can configure additional router instances, which are automatically treated
as Level 1 areas. You must configure the parameters for each instance of the IS-IS routing process individually.
For IS-IS multiarea routing, you can configure only one process to perform Level 2 routing, although you can define up
to 29 Level 1 areas for each Cisco unit. If Level 2 routing is configured on any process, all additional processes are
automatically configured as Level 1. You can configure this process to perform Level 1 routing at the same time. If Level 2
routing is not desired for a router instance, remove the Level 2 capability using the is-type global configuration
command. Use the is-type command also to configure a different router instance as a Level 2 router.
This section briefly describes how to configure IS-IS routing. For more detailed information about IS-IS, see the IS-IS
documents listed in the
This section includes the following topics:

Default IS-IS Configuration, page 872

Nonstop Forwarding Awareness, page 872

Configuring IS-IS Global Parameters, page 875
Related Documents, page 924.
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Related Documents, page 924.