LDP over non-directly connected links

Unanswered Question
May 24th, 2008


I have a question regarding LDP. The normal practice for running LDP is over directly connected links.

Is there any way of running this over a cloud.

Lets say there are 5 routers A,B,C,D,E connected in series. Is there any way to run LDP between A and E ?

IPsec or mpls l2tp tunnels ? ethernet dot1q double tagging etc ?


Jabran Zahid

I have this problem too.
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dara111983 Sun, 05/25/2008 - 10:02

Hi Zahid,

Surely yes,

The directed/targetted LDP session has many applications which we have currently deployed on the MPLS cloud between the two LSR's.

One such an example can be found here: http://www.cisco.com/en/US/docs/ios/mpls/configuration/guide/mp_ldp_sessn_prot_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1027258

This is only for protection from the LDP session failure between the two LSR's.


n.nandrekar Mon, 05/26/2008 - 23:48

Hi Jabran,

Yes, you can surely run LDP over indirectly connected routers. There are two things :

1. Run Targetted LDP where you specify the remote LDP neighbor. The tcp session if formed directly with the neighbor to form an LDP session.

USE: This can be used to exchange the vpn labels or in cases where you already have a mpls path accross rsvp etc. There is no point exchanging labels with 2 indirectly connected routers if the middle routers know nothing about it and are not running mpls.

2. You can use MPLSoGRE (supported on 6500). In this scenario you can form a gre tunnel between the indirectly connected routers and start ldp (mpls ip) over that tunnel interface. The neighbor is detected in the same way as directly connected and the GRE tunnel is used to send the mpls packets.

USE : This can be used to connect 2 MPLS clouds over a ip cloud or to provide MPLS VPN service where the PE are MPLS aware while the P routers are pure IP routers.

For more details on MPLSoGRE, refer :





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