When you configure several RSVP LSPs to the same egress router, the LSP with the lowest metric is selected and carries all traffic. If all of the LSPs have the same metric, one of the LSPs is selected at random and all traffic is forwarded over it. To distribute traffic equally across all LSPs, you can configure load balancing on the ingress or transit routers, depending on the type of load balancing configured.
Figure 10 illustrates an MPLS network with four LSPs configured to the same egress router (R0). Load balancing is configured on ingress router R1. The example network uses Open Shortest Path First (OSPF) as the interior gateway protocol (IGP) with OSPF area 0.0.0.0. An IGP is required for the Constrained Shortest Path First (CSPF) LSP, which is the default for the JUNOS software. In addition, the example network uses a policy to create BGP traffic.
Figure 10: Load-Balancing Network Topology
The network shown in Figure 10 consists of the following components:
The network shown in Figure 10 is a BGP full-mesh network. Since route reflectors and confederations are not used to propagate BGP learned routes, each router must have a BGP session with every other router running BGP.
For complete configurations for all routers in the example MPLS network, see Router Configurations for the Load-Balanced MPLS Network.
For a description of the situation before and after load balancing is configured in the network to use all four LSPs to forward traffic, see Traffic Flows Before Load Balancing.
