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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Configuring IP Unicast Routing
Configuring ISO CLNS Routing
Nonstop Forwarding Awareness
The integrated IS-IS NSF Awareness feature is supported for IPv4, beginning with Cisco IOS
Release 12.2(25)SEG. The feature allows customer premises equipment (CPE) routers that are
NSF-aware to help NSF-capable routers perform nonstop forwarding of packets. The local router is not
necessarily performing NSF, but its awareness of NSF allows the integrity and accuracy of the routing
database and link-state database on the neighboring NSF-capable router to be maintained during the
switchover process.
This feature is automatically enabled and requires no configuration. For more information on this
feature, see the Integrated IS-IS Nonstop Forwarding (NSF) Awareness Feature Guide.
Enabling IS-IS Routing
To enable IS-IS, you specify a name and NET for each routing process. You then enable IS-IS routing
on the interface and specify the area for each instance of the routing process.
Beginning in privileged EXEC mode, follow these steps to enable IS-IS and specify the area for each
instance of the IS-IS routing process:
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
clns routing Enable ISO connectionless routing on the switch.
Step 3
router isis [area tag] Enable the IS-IS routing for the specified routing process and enter IS-IS
routing configuration mode.
(Optional) Use the area tag argument to identify the area to which the IS-IS
router is assigned. You must enter a value if you are configuring multiple
IS-IS areas.
The first IS-IS instance configured is Level 1-2 by default. Later instances
are automatically Level 1. You can change the level of routing by using the
is-type global configuration command.
Step 4
net network-entity-title Configure the NETs for the routing process. If you are configuring
multiarea IS-IS, specify a NET for each routing process. You can specify a
name for a NET and for an address.
Step 5
is-type {level-1 | level-1-2 |
level-2-only}
(Optional) You can configure the router to act as a Level 1 (station) router,
a Level 2 (area) router for multi-area routing, or both (the default):
• level-1—act as a station router only
• level-1-2—act as both a station router and an area router
• level 2—act as an area router only
Step 6
exit Return to global configuration mode.
Step 7
interface interface-id Specify an interface to route IS-IS, and enter interface configuration mode.
If the interface is not already configured as a Layer 3 interface, enter the no
switchport command to put it into Layer 3 mode.
Step 8
ip router isis [area tag] Configure an IS-IS routing process for ISO CLNS on the interface and
attach an area designator to the routing process.
Step 9
clns router isis [area tag] Enable ISO CLNS on the interface.
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