Verifying the IP and IGP Layers
Problem
After you have configured the label-switched path (LSP), issued the show mpls lsp extensive command, and determined that there is an error, you might find that the error is not in the physical or data link layers. Continue investigating the problem at the IP and IGP layers of the network.
Figure 1 illustrates the IP and IGP layers of the layered MPLS model.
Figure 1: IP and IGP Layers
Solution
At the IP and IGP layers, you must check the following:
- Interfaces have correct IP addressing, and the IGP neighbors or adjacencies are established.
- Open Shortest Path First (OSPF) or Intermediate System-to-Intermediate
System (IS-IS) protocols are configured and running correctly.
- If the OSPF protocol is configured, check the IP layer first, then the OSPF configuration, making sure that the protocol, interfaces, and traffic engineering are configured correctly.
- If the IS-IS protocol is configured, it doesn’t
matter whether you check IS-IS or IP first because both protocols
are independent of each other. Verify that IS-IS adjacencies are up,
and that the interfaces and IS-IS protocol are configured correctly.
Note: The IS-IS protocol has traffic engineering enabled by default.
If the network is not functioning at the IP or IGP layers, the LSP does not work as configured.
Figure 2 illustrates the MPLS network used in this topic.
Figure 2: MPLS Network Broken at the IP and IGP Layers
The network shown in Figure 2 is a fully meshed configuration where every directly connected interface can receive and send packets to every other similar interface. The LSP in this network is configured to run from ingress router R1, through transit router R3, to egress router R6. In addition, a reverse LSP is configured to run from R6, through R3, to R1, creating bidirectional traffic. The crosses in Figure 2 indicate where the LSP is not working because of the following problems at the IP and IGP layer:
- An IP address is configured incorrectly on the ingress router (R1).
- The OSPF protocol is configured with a router ID (RID) but without the loopback (lo0) interface, and traffic engineering is missing from the transit router (R3).
- Levels in the IS-IS network are mismatched.
