# Configuring LDP FEC Deaggregation

Beginning with JunosE Release 8.1.0, LDP routers running JunosE employ LDP FEC aggregation by default. FEC aggregation means that when an LDP egress router advertises multiple prefixes, all the prefixes are members of the same FEC. Only a single label is advertised for this FEC. LDP maintains this aggregation as the advertisement traverses the network, if possible.

Consider the topology shown in Figure 62.

Figure 62: FEC Aggregation and Equal-Cost Paths

In this example, LSR 2 uses FEC aggregation, but LSR 3 does not. Consequently, LSR 2 advertises the single label e, mapped to a FEC that includes both prefixes, 10.10.22.0/24 and 10.43.12.0/24.

In contrast, LSR 3 has two FECs, one for 10.10.22.0/24 and one for 10.43.12.0/24. A separate label is bound to each FEC. LSR 3 advertises label h for one FEC and label w for the other FEC.

LSR 2 and LSR 3 are downstream routers for LSR 1. LSR 1 does not aggregate. Instead, LSR 1 advertises label d for 10.10.22.0/24 and label x for 10.43.12.0/24.

To configure MPLS LDP FEC deaggregation to bind each prefix on the current virtual router to a separate label:

- Issue the mpls ldp deaggregate command:
  host1(config)#mpls ldp deaggregate

#### Related Documentation

- Basic MPLS Configuration Tasks
- Additional LDP Configuration Tasks
- mpls ldp deaggregate