BGP Signaling for VPLS PE Routers Overview

BGP can autonomously signal pseudowires between the PE routers participating in the same virtual private LAN service (VPLS) network. As PE routers are added to and removed from the VPLS network, BGP can signal pseudowires to new PE routers and tear down old pseudowires to old PE routers. Each PE router only needs to be configured with the identity of the VPLS routing instance. Each PE router does not need to be configured with the identities of all of the PE routers that are or might become a part of the VPLS network.

There are three primary ways to signal a virtual private LAN service (VPLS) VPN in an MPLS network. You can power the VPLS using the BGP control plane, or using the LDP control plane, or using a method called FEC 129 which combines both methods of signaling.

One advantage of the BGP control plane is the ability for a provider edge (PE) router to automatically discover any other PE routers that take part in a given VPLS VPN. This is possible thanks to the exchange of route target information that identifies whether a router participates in a particular VPN. The result is that BGP can autonomously signal pseudowires between the PE routers participating in the same VPLS. This is in contrast to an LDP-signaled VPLS, where remote PEs must be defined explicitly.

As PE routers are added to and removed from the VPLS network, BGP can signal pseudowires to new PE routers. Similarly, BGP can tear down old pseudowires to old PE routers where the VPLS instance has been removed. Each PE router only needs to be configured with the relevant route target information of the VPLS routing instance. There is no need to configure neighbor PEs explicitly.

Note that all of this is completely independent of the choice of protocol to signal the transport label-switched paths (LSPs) that carry the VPN packets between PEs. For example, you are free to choose LDP, RSVP, SR-MPLS, or static LSPs. The choice of transport LSP protocol is entirely separate from the choice of VPLS signaling protocol. This is true of all methods of VPLS signaling.