Verifying the IP Layer

Purpose

You can check the IP layer before or after you check the IGP layer, depending on whether you have OSPF or IS-IS configured as the IGP. If your MPLS network is configured with OSPF as the IGP, you must first verify the IP layer, checking that the interfaces have correct IP addressing and that the OSPF neighbors are established before you check the OSPF layer.

If you have IS-IS configured as the IGP in your MPLS network, you can verify either the IP layer or the IS-IS protocol layer first. The order in which you check the IP or IS-IS layer does not affect the results.

Figure 16: MPLS Network Broken at the IP Layer

The cross in Figure 16 indicates where the LSP is broken because of the incorrect configuration of an IP address on ingress router R1.

Steps To Take

To check the IP layer, follow these steps:

1. Verify the LSP
2. Verify IP Addressing
3. Verify Neighbors or Adjacencies at the IP Layer
4. Take Appropriate Action
5. Verify the LSP Again