Im just starting to work on MPLS and I have a few questions about LDP and MPLS VPNs. Hopefully some expert out there can show me if my thinking is correct.
Q1. If I have a number of directly connected PE routers (say via ethernet) which are servicing MPLS VPNs, technically do i really need to run LDP here ? I believe the LFIB gets populated by MBGP for the VPNv4 customer prefixes, so is there any need for LDP between the directly connected PEs ?
Q2. In the case where now I have another set of PEs that are not directly connected to the set of PEs in Q1, and I have a P router to connect the two sets of PEs together. Am I correct in saying that now I must run LDP even if I am just doing MPLS VPNs, since the P router needs to know how to forward traffic, and it does this forwarding via LDP since it doesnt particiapte in MBGP and therefre does not have customer VPNv4 routes/prefixes ?
Q3. I read about LDP session protection via targetted LDP. If P/PEs are directly connected (via ethernet), is there any point in running protected LDP sessions ? Im thinking of having two interfaces on each router, ethernet interface 1 (g0/1) and ethernet interface 2 (g0/2). So each router g0/1 will be directly connected via an ethernet switch, and same for g0/2. If we run LDP between loopbacks of the routers, then there is inherent protection if one of the interfaces (say g0/1) goes down, the LDP session does not go down, since the loopbacks will be reachable via the other g0/2 interface ? So in this case is there any point in using session protection ?
Completely correct. That's why you need the RD. You can also try debugging it - if you don't specify the RD then the value 0:0 will be taken and you can nicely simulate one network jumping from one VRF to another if you add it to one VRF first, and then to another.