Checking the RSVP Layer
Purpose
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, data link, or Internet Protocol (IP) and interior gateway protocol (IGP) layers. Continue investigating the problem at the RSVP layer of the network.
Figure 19 illustrates the RSVP layer of the layered MPLS model.
With this layer, you check that dynamic RSVP signaling is occurring as expected, neighbors are connected, and interfaces are configured correctly for RSVP. Check the ingress, egress, and transit routers.
If the network is not functioning at this layer, the LSP does not work as configured.
Figure 20 illustrates the MPLS network used in this chapter.
The network shown in Figure 20 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.
However, in this example, the LSP is down without a path in either direction, from R1 to R6 or from R6 to R1.
The crosses shown in Figure 20 indicate where the LSP is broken. Some possible reasons the LSP is broken might include that dynamic RSVP signaling is not occurring as expected, neighbors are not connected, or interfaces are incorrectly configured for RSVP.
In the network in Figure 20, a configuration error on transit router R3 prevents the LSP from traversing the network as expected.