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11.6 Controlling DIS Election<br />

Problem<br />

You want to force IS-IS to use a specific router as the designated router.<br />

Solution<br />

Increase the priority on the desired router:<br />

[edit protocols isis]<br />

aviva@RouterH# set interface fe-0/0/1 level 2 priority 65<br />

<strong>Discussion</strong><br />

With the IS-IS configuration we have shown in previous recipes, all IS-IS routers<br />

have the default priority value (64), which IS-IS uses to elect the DR in each area. In<br />

this situation, the router with the higher MAC address is elected as the DR.<br />

In the previous recipes, RouterG is elected DR because it has a higher MAC address<br />

(0:5:85:c2:2e:d1, compared to 0:5:85:c1:d1:d1 for RouterH):<br />

aviva@RouterG> show isis adjacency<br />

Interface System L State Hold (secs) SNPA<br />

fe-0/0/1.0 RouterH 2 Up 7 0:5:85:c1:d1:d1<br />

fe-1/0/0.0 Captain-Caveman1 Up 7 0:5:85:ca:ca:70<br />

aviva@RouterH> show isis adjacency<br />

Interface System L State Hold (secs) SNPA<br />

fe-0/0/1.0 RouterG 2 Up 20 0:5:85:c2:2e:d1<br />

fe-1/0/1.0 RouterA 1 Up 7 0:5:85:ca:e7:d0<br />

Looking at the IS-IS interfaces, you see the default priority value of 64 for all interfaces<br />

at both Level 1 and Level 2 and that RouterG is the DR for the Level 2 area:<br />

aviva@RouterG> show isis interface detail<br />

IS-IS interface database:<br />

fe-0/0/1.0<br />

Index: 64, State: 0x6, Circuit id: 0x2, Circuit type: 3<br />

LSP interval: 100 ms, CSNP interval: 10 s<br />

Level Adjacencies Priority Metric Hello (s) Hold (s) Designated Router<br />

1 0 64 10 9.000 27<br />

2 1 64 10 3.000 9 RouterG.02 (us)<br />

fe-1/0/0.0<br />

Index: 68, State: 0x6, Circuit id: 0x3, Circuit type: 1<br />

LSP interval: 100 ms, CSNP interval: 10 s<br />

Level Adjacencies Priority Metric Hello (s) Hold (s) Designated Router<br />

1 1 64 10 9.000 27 RouterA.02<br />

(not us)<br />

lo0.0<br />

Index: 70, State: 0x6, Circuit id: 0x1, Circuit type: 0<br />

LSP interval: 100 ms, CSNP interval: disabled<br />

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

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

Controlling DIS Election | 365

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