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RouterA.02-00 0x59 0xeda9 632 L1 L2<br />

3 LSPs<br />

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

LSP ID<br />

Sequence Checksum Lifetime Attributes<br />

RouterH.00-00 0x61 0xa315 923 L1 L2<br />

RouterG.00-00 0x61 0x125e 741 L1 L2<br />

RouterG.02-00 0x5e 0x79f0 741 L1 L2<br />

3 LSPs<br />

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

IS-IS routers exchange LSPs that describe each individual router’s view of the network<br />

topology and they store the LSPs in a link-state database. The SPF algorithm<br />

then runs on the link-state database to create the IS-IS routing table. Use the show<br />

isis database command to look at the contents of the link-state database. In this recipe,<br />

RouterG is a Level 1–Level 2 router, so you see two link-state databases, one for<br />

each level.<br />

The first part of the output shows that the Level 1 link-state database has three LSPs.<br />

The entry for RouterG includes the attach bit (Attached), which indicates that it is<br />

connected to another IS-IS area. From the configuration, you know that this router is<br />

connected to area 30.<br />

If you check on the other Level 2 router, its Level 2 database is identical to that of<br />

RouterG:<br />

aviva@RouterH> show isis database level 2<br />

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

LSP ID<br />

Sequence Checksum Lifetime Attributes<br />

RouterH.00-00 0x61 0xa315 988 L1 L2<br />

RouterG.00-00 0x61 0x125e 802 L1 L2<br />

RouterG.02-00 0x5e 0x79f0 802 L1 L2<br />

3 LSPs<br />

Use the extensive version of the show isis database command to see all the information<br />

carried in the LSP:<br />

aviva@RouterG> show isis database extensive level 2 RouterH.00-00<br />

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

RouterH.00-00 Sequence: 0x62, Checksum: 0xa116, Lifetime: 1121 secs<br />

IS neighbor: RouterG.02 Metric: 10<br />

IP prefix: 10.0.1.0/24 Metric: 10 Internal Up<br />

IP prefix: 10.0.24.0/24 Metric: 10 Internal Up<br />

Header: LSP ID: RouterH.00-00, Length: 134 bytes<br />

Allocated length: 284 bytes, Router ID: 192.168.18.1<br />

Remaining lifetime: 1121 secs, Level: 2,Interface: 64<br />

Estimated free bytes: 170, Actual free bytes: 150<br />

Aging timer expires in: 1121 secs<br />

Protocols: IP, IPv6<br />

Packet: LSP ID: RouterH.00-00, Length: 134 bytes, Lifetime : 1198 secs<br />

Checksum: 0xa116, Sequence: 0x62, Attributes: 0x3 <br />

NLPID: 0x83, Fixed length: 27 bytes, Version: 1, Sysid length: 0 bytes<br />

Packet type: 20, Packet version: 1, Max area: 0<br />

Viewing the IS-IS Link-State Database | 357<br />

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

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

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