mpls ldp discovery transport-address

I am tyring to rationalize the use of the the "mpls ldp discovery transport-address interface fa0/1" while using the "mpls neigh" command between R4 and R6.

If the ldp discovery command is used isn't the tcp session established with the interface address instead of the loopback?  Then why wouldn't the neighbor command reflect the neighbors interface address as well?  How is the loopback address involved in the ldp session establishment if the configuration forces the use of the interface address?


many thanks,



  • I think in this instance the use of neighbor command reflects the Router-ID that identifies the neighbor rather than the address used to establish the tcp session.  Normally they would be one and the same, but the use of the "mpls ldp discovery transport-address interface command" changes how the tcp session is established but doesn't affect the Router-ID by which either the neighbor or the local router identifies itself. (Useful if say the ip of the loopback used as the Router-ID was unreachable for some reason)


  • Hi,


    In this case , we need to use LDP Authentication on loopback address or on interface IP address?

    But I found , while apply to interface is faster for making LDP session up. Than on loopback..

    What should the best method as per best practice?

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