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11.5 Configuring a Level 1–Only Router<br />

Problem<br />

You want to set up the Level 1–only routers.<br />

Solution<br />

For routers that participate only in a Level 1 area, disable Level 2 on the router:<br />

[edit protocols isis]<br />

aviva@RouterA# set level 2 disable<br />

aviva@RouterA# set interface fe-0/0/0.0<br />

aviva@RouterA# set interface lo0.0<br />

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

To configure routers that are only in a Level 1 area, just disable Level 2 routing for all<br />

of IS-IS, not for a specific interface. The configuration looks like this:<br />

[edit protocols]<br />

aviva@RouterA# show<br />

isis {<br />

level 2 disable;<br />

interface fe-0/0/0.0;<br />

interface lo0.0;<br />

}<br />

These routers have only a Level 1 link-state database:<br />

aviva@RouterA> show isis database<br />

IS-IS level 1 link-state database:<br />

LSP ID<br />

Sequence Checksum Lifetime Attributes<br />

RouterG.00-00 0x198 0x3ea3 2389 L1 L2 Attached<br />

RouterA.00-00 0x1ad 0xee5f 1190 L1<br />

RouterA.02-00 0x1a6 0x4efc 1190 L1<br />

3 LSPs<br />

IS-IS level 2 link-state database:<br />

0 LSPs<br />

The Level 1 link-state database has three LSPs, while the Level 2 database is empty.<br />

Level 1 IS-IS routers know only about paths to routers within their level. For routes<br />

outside the level, they install a default route that points to the closest Level 1–Level 2<br />

router. To confirm that the router knows about other levels, first check the link-state<br />

database for an LSP that has the Attached (ATT) bit set. The show isis database output<br />

above shows that RouterG is connected to another level:<br />

LSP ID<br />

Sequence Checksum Lifetime Attributes<br />

RouterG.00-00 0x198 0x3ea3 2389 L1 L2 Attached<br />

Configuring a Level 1–Only Router | 363<br />

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

Copyright © 2008 O’Reilly & Associates, Inc. All rights reserved.

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