Step 2: Verify IP Addressing

Purpose

When you investigate the IP layer, you verify that interfaces have correct IP addressing, and that OSPF neighbors or IS-IS adjacencies are established. In this example, an IP address is configured incorrectly on the ingress router (R1).

Action

To verify IP addressing, enter the following command from the ingress, transit, and egress routers:

user@host> show interfaces terse

Sample Output

user@R1> show interfaces terse

Interface               Admin Link Proto Local                 Remote

so-0/0/0                up    up  

so-0/0/0.0              up    up   inet  10.1.12.1/30    

                                   iso  

                                   mpls 

so-0/0/1                up    up  

so-0/0/1.0              up    up   inet  10.1.15.1/30    

                                   iso  

                                   mpls 

so-0/0/2                up    up  

so-0/0/2.0              up    up   inet  10.1.13.2 <<< Incorrect IP address

                                   iso  

                                   mpls 

lo0                     up    up  

lo0.0                   up    up   inet  10.0.0.1 

                                   iso   49.0004.1000.0000.0001.00

user@R3> show interfaces terse

Interface               Admin Link Proto Local                 Remote

so-0/0/0                up    up

so-0/0/0.0              up    up   inet  10.1.34.1/30    

                                   iso  

                                   mpls 

so-0/0/1                up    up  

so-0/0/1.0              up    up   inet  10.1.23.2/30    

                                   iso  

                                   mpls 

so-0/0/2                up    up  

so-0/0/2.0              up    up   inet  10.1.13.2/30 <<< Identical to R1

                                   iso  

                                   mpls 

so-0/0/3                up    up  

so-0/0/3.0              up    up   inet  10.1.36.1/30    

                                   iso  

                                   mpls 

lo0                     up    up  

lo0.0                   up    up   inet  10.0.0.3 

                                   iso   49.0004.1000.0000.0003.00

user@R6> show interfaces terse

Interface               Admin Link Proto Local                 Remote

so-0/0/0                up    up  

so-0/0/0.0              up    up   inet  10.1.56.2/30    

                                   iso  

                                   mpls 

so-0/0/1                up    up

so-0/0/1.0              up    up   inet  10.1.46.2/30    

                                   iso  

                                   mpls 

so-0/0/2                up    up  

so-0/0/2.0              up    up   inet  10.1.26.2/30    

                                   iso  

                                   mpls 

so-0/0/3                up    up  

so-0/0/3.0              up    up   inet  10.1.36.2/30    

                                   iso  

                                   mpls 

lo0.0                   up    up   inet  10.0.0.6 

                                   iso   49.0004.1000.0000.0006.00

What It Means

The sample output shows that the IP addresses for interface so-0/0/2.0 on R1 and interface so-0/0/2.0 on R3 are identical. Interface IP addresses within a network must be unique for the interface to be identified correctly.