Targeted LDP over l2VPN

[imadhassan]

Hi, we are running l2VPN between 2 PEs and the traffic between them is forwarding over TE tunnel. LDP is not running on any of the interface of PE routers.

My question is why the LDP session is showing as "UP" on pseudowire connection b/w the PEs ? What is the logic behind this ?

Below is my show output on one of my PE router:

PE-A#sh mpls l2transport vc 97 detail
Local interface: Se2/0 up, line protocol up, HDLC up
  Destination address: 10.5.0.9, VC ID: 97, VC status: up
    Output interface: Tu97, imposed label stack {16011 19}
    Preferred path: not configured  
    Default path: active
    Next hop: point2point
  Create time: 03:18:12, last status change time: 01:18:09
  Signaling protocol: LDP, peer 10.5.0.7:0 up
    Targeted Hello: 10.5.0.9(LDP Id) -> 10.5.0.7
    Status TLV support (local/remote)   : enabled/supported
      Label/status state machine        : established,

[medhat elsaeed]

Hello,

AToM uses one MPLS label to identify the AToM VCs (VC label). Therefore it needs a protocol to signal this VC label ( which is LDP for Cisco ATOM ) "Martini Draft "

and due to that the two PE routers mostly aren't directly connected it uses Targeted LDP hello to establish the LDP neighbor-ship between the two PE routers  to be able to exchange the VC labels.

Regards.

[pabloboscariol]

the logic is that the ldp targeted session is not inside the PW. Is used to establish the PW. The PE routers needs to know which label is the other end PE expecting for this PW.

So based on the "lower layer" mpls (rsvp, or ldp), the PE router has a transport label to reach the opposite end PE (first layer of the stack), and using this targeted session (it doesn't need to be a directly connected router) the PE get the second label to create the stack.

Have a great day!