LDP - LFIB Problem

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Jul 26th, 2009
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If two routers are forming LDP neighbor relationship but no label swapping is taking place.

Is is due to CEF or anything to do with BGP relationship between these neighbors.

Please share the experience.

Thanks in advance


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amit.bhagat Sun, 07/26/2009 - 15:41
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Hi Subodh,

no Labels are assigned to BGP routes. Labels are only assigned to directly connected routes and IGP-learned routes.

Please share your topology here.

shivlu jain Sun, 07/26/2009 - 22:14
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Hi Subodh

You can also assign the labels with the help of BGP with in case of your scenario it is not required. If the basic configs are properly configured then it might be the issue of CEF. Please post the outputs of show mpls forwarding-table.


shivlu jain

amit.bhagat Sun, 07/26/2009 - 23:03
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Hi Shivlu,

Of course, labels are assigned to BGP routes but only in MPLS VPN case running MP-iBGP.

Giuseppe Larosa Mon, 07/27/2009 - 23:41
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Hello Amit,

>> Of course, labels are assigned to BGP routes but only in MPLS VPN case running MP-iBGP.

in some inter-AS or CSC scenarios you can use BGP to exchange labels the so called BGP with labels but it is an advanced topic.

usually if CEF is not enabled when you try to do sh mpls forwarding it clearly states CEF not running.

There are then some specific issues for example when using loopbacks for testing purposes with OSPF as IGP:

OSPF will try to advertise a /32 unless you configure

int loop m

ip ospf network point-to-point

LDP labels are installed if a corresponding prefix is found in CEF table and with the same outgoing interface/ IP next hop.

Hope to help


amit.bhagat Tue, 07/28/2009 - 15:41
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Hi Giuseppe,

I am aware of Inter-AS/CSC where labels are forwarded using neighbor send-label command.

In MP-eBGP (in case of BGP Confederation implementation), new labels can be assigned using next-hop-self command.

Actually, I replied keeping into perspective a single AS. I guess, I should have been more specific.


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