Examine the Link-State Database
Purpose
You can examine the entire link-state database to obtain important information about the network. In this step, you verify that the key word Attached appears in the output of the Level 1 routers (R3 and R4) and the Level 1/Level 2 routers (R2 and R5).
Action
To examine the link-state database for routers at different levels of the network, enter the following CLI command:
Sample Output
user@R1> show isis database
IS-IS level 1 link-state database: 0 LSPs IS-IS level 2 link-state database: LSP ID Sequence Checksum Lifetime Attributes R1.00-00 0x1b 0xd4b5 583 L1 L2 R2.00-00 0x1d 0x1a4f 1131 L1 L2 R5.00-00 0x1b 0x6245 883 L1 L2 R6.00-00 0x20 0xf7c 919 L1 L2 4 LSPs user@R2> show isis database IS-IS level 1 link-state database: LSP ID Sequence Checksum Lifetime Attributes R2.00-00 0x56 0xbd8c 862 L1 L2 Attached R3.00-00 0x58 0xaca1 463 L1 2 LSPs IS-IS level 2 link-state database: LSP ID Sequence Checksum Lifetime Attributes R1.00-00 0x57 0x3e10 871 L1 L2 R2.00-00 0x5e 0x9790 1150 L1 L2 R5.00-00 0x5a 0xadba 1162 L1 L2 R6.00-00 0x56 0xa2b2 484 L1 L2 4 LSPs user@R3> show isis database IS-IS level 1 link-state database: LSP ID Sequence Checksum Lifetime Attributes R2.00-00 0x56 0xbd8c 792 L1 L2 Attached R3.00-00 0x58 0xaca1 397 L1 2 LSPs IS-IS level 2 link-state database: 0 LSPs [edit protocols isis] user@R4> show isis database IS-IS level 1 link-state database: LSP ID Sequence Checksum Lifetime Attributes R4.00-00 0x56 0x34b8 1125 L1 R5.00-00 0x57 0x22bb 795 L1 L2 Attached 2 LSPs IS-IS level 2 link-state database: 0 LSPs user@R5> show isis database IS-IS level 1 link-state database: LSP ID Sequence Checksum Lifetime Attributes R4.00-00 0x56 0x34b8 1071 L1 R5.00-00 0x57 0x22bb 745 L1 L2 Attached 2 LSPs IS-IS level 2 link-state database: LSP ID Sequence Checksum Lifetime Attributes R1.00-00 0x57 0x3e10 707 L1 L2 R2.00-00 0x5e 0x9790 982 L1 L2 R5.00-00 0x5a 0xadba 1002 L1 L2 R6.00-00 0x57 0xa0b3 1064 L1 L2 4 LSPs user@R6> show isis database IS-IS level 1 link-state database: 0 LSPs IS-IS level 2 link-state database: LSP ID Sequence Checksum Lifetime Attributes R1.00-00 0x1b 0xd4b5 728 L1 L2 R2.00-00 0x1c 0x1c4e 604 L1 L2 R5.00-00 0x1b 0x6245 1032 L1 L2 R6.00-00 0x20 0xf7c 1072 L1 L2 4 LSPs
Meaning
The sample output shows the details of the Level 1 and Level 2 IS-IS databases for Routers R1, R2, R3, R4, R5, and R6. Whether a router is configured for Level 1, Level 2, or Level 1/Level 2 is indicated by the type of IS-IS link-state datebase(s) in the output for the show isis database command for that router. For example, R3 and R4 are Level 1 routers because they do not have link-state PDUs in the Level 2 link-state database, and R1 and R6 are Level 2 routers because they do not have link-state PDUs in the Level 1 link-state database. R2 and R5 are have link-state PDUs in both Level 1/Level 2 link-state databases, indicating they are Level 1/Level 2 routers.
In addition, the output for R2 shows that it is a Level 1/Level 2 router because it has R3 in its Level 1 database, while R3 does not have the L2 notation in the Attributes field, indicating that it is configured for Level 1.
The details of the Level 2 IS-IS database are the same for all Level 2 routers in the network.
The key word Attached appears in the Level 1 link-state database for R2, R3, R4, and R5, indicating that the Level 2 routers (R2 and R5) can communicate with other Level 2 systems and act as gateways for the Level 1 routers (R3 and R4) in their respective areas. If the links that connect R2 and R5 to the other Level 2 routers (R1 and R6) are broken, the key word Attached will not appear in the output because R2 and R5 will no longer act as gateways for the Level 1 routers.
