Step 3: Verify the IS-IS Configuration

Purpose

When you have determined that the problem is probably at the IS-IS protocol level, check the IS-IS configuration of the routers in your network.

Action

To verify the IS-IS configuration, enter the following command from the relevant routers:

user@host> show configuration protocols isis

Sample Output

user@R1> show configuration protocols isis 

level 1 disable;

interface so-0/0/0.0;

interface so-0/0/1.0;

interface so-0/0/2.0;

interface lo0.0; {

    passive

user@R3> show configuration protocols isis 

level 1 disable;

interface all {

    level 2 metric 10;

}

interface fxp0.0 {

    disable;

}

interface lo0.0; {

    passive

user@R6> show configuration protocols isis    

level 2 disable;                        <<< Incorrect level disabled

interface all {

    level 2 metric 10;

}

interface fxp0.0 {

    disable;

}

interface lo0.0; {

    passive

What It Means

The sample output shows that R6 has Level 2 disabled, while R1 and R3 have Level 1 disabled. For IS-IS adjacencies to establish, routers need to be at the same level. Another common configuration error is to omit the loopback (lo0) interface from the configuration at the [edit protocols isis] hierarchy level. IS-IS does not function correctly if the loopback (lo0) interface is not configured at this level. In addition, including the passive statement ensures that protocols are not run over the loopback (lo0) interface and the loopback (lo0) interface is advertised correctly throughout the network.