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RouterA<br />

Level 2<br />

RouterB<br />

Level 2<br />

RouterC<br />

Level 2<br />

Area 1<br />

RouterF<br />

Level 1/2<br />

RouterG<br />

Level 1/2<br />

RouterD<br />

Level 1/2<br />

Area 3<br />

RouterE<br />

Level 1<br />

10.0.21.2<br />

RouterH<br />

Level 1<br />

RouterI<br />

Level 1<br />

Area 2<br />

Figure 11-2. IS-IS topology for leaking routes from Level 2 to Level 1<br />

You do this is by creating a routing policy on RouterG that leaks the route to the<br />

external network 10.0.21.0/24 into the Level 1 routers in Area 2. The policy in this<br />

recipe contains a route filter that matches all /32 addresses in this external network<br />

and redistributes all IS-IS Level 2 routes from the network into IS-IS Level 1. Matching<br />

the /32 addresses captures all the addresses you are interested in, which are the<br />

loopback addresses. After you apply the policy on the Level 1–Level 2 router, you see<br />

on RouterH, the Level 1 router, that the route to 10.0.21.0/24 has leaked into its<br />

routing table:<br />

aviva@RouterH> show route 10.0.21.2<br />

inet.0: 12 destinations, 12 routes (12 active, 0 holddown, 0 hidden)<br />

+ = Active Route, - = Last Active, * = Both<br />

10.0.21.0/24 *[IS-IS/18] 00:00:09, metric 40<br />

> to 10.0.8.1 via fe-0/0/1.0<br />

Instead of having a cost of 15, which is the default cost of an intra-area IS-IS route,<br />

the route has a cost of 18, which is the default for an interarea IS-IS route.<br />

11.10 Adjusting IS-IS Link Costs<br />

Problem<br />

You want to direct traffic within an IS-IS area toward a particular router.<br />

This is the Title of the Book, eMatter Edition<br />

Copyright © 2008 O’Reilly & Associates, Inc. All rights reserved.<br />

Adjusting IS-IS Link Costs | 373

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