LDP Tunnelling within RSVP

LDP Tunnelling is a feature that could be used in a scenario where certain aspects of a provider network might not support RSVP, or perhaps the provider itself may have a desire not to deploy RSVP within certain areas of their network.

I have seen cases of this where a provider wishes to have simplicity in certain areas of their network, in regional areas, or areas that do not require any of the advanced traffic engineering features that RSVP offers.

For this purpose it’s possible to tunnel an LDP LSP within an RSVP signalled LSP. For example a PE on the regional edge of a provider network would terminate an LDP session on one interface, and tunnel the LDP session through a core, RSVP facing interface.

From a control plane perspective the tunnelled MPLS frame is stacked with three labels when it enters the RSVP tunnel. One label is the inner VPN label, the second is the outer LDP label, and the top label is outer RSVP label that transport the packet into the providers RSVP core.

Configuration Step 1

Targetted LDP must be configured and enabled on the PE interface that faces the remote device.

 protocols {

     ldp {
          interface ge-0/0/0;
          interface le0.0;
     }
}

Configuration Step 2

An active LSP must exist within RSVP, with the addition of the ldp-tunneling knob.

protocols {
     mpls {
          label-switched-path P1_to_P3 {
               to 10.10.10.3;
               ldp-tunneling;
               no-cspf;
          }
     interface all;
}