LDP overview

Each Link Switch Router (LSR) establishes a peer relationship with the neighboring LDP-enabled routers and exchanges label mapping information. This label mapping information is stored in an LDP database on each LSR. When an LSR determines that one of the peers is the next-hop for a FEC, the LSR uses the label mapping information from the peer to set up an LSP that is associated with the FEC.

The devices advertise their loopback addresses to their LDP peers as a 32-bit prefix-type FEC. When an LSR installs a label for a FEC, it also creates an MPLS tunnel route, which is then made available to routing applications. This allows each router to potentially be an ingress LER for an LSP whose destination is the device's loopback address.

The result of an LDP configuration is a full mesh of LSPs in an MPLS network, with each LDP-enabled router a potential ingress, transit, or egress LSR, depending on the destination.

The system supports LDP for the configuration of non-traffic-engineered tunnel LSPs in an MPLS network. LDP is described in RFC 5036.

The LDP label space ID has a default value of zero which improves interoperability with routers from other vendors.