Step 4: 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:

user@host> show isis database

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

What It Means

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 LSPs in the Level 2 link-state database, and the R1 and R6 are Level 2 routers because they do not have LSPS in the Level 1 link-state database. R2 and R5 are have LSPs 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.