[c-nsp] LDP sessions established to non directly connected routers, when new link is activated

James Bensley jwbensley at gmail.com
Thu Sep 24 09:37:33 EDT 2015


On 24 September 2015 at 10:51, Dan Peachey <dan at illusionnetworks.com> wrote:
> On 22 September 2015 at 23:59, CiscoNSP List <CiscoNSP_list at hotmail.com>
> wrote:
>
>> Hi Everyone,
>>
>>
>>
>> Bit of a strange one.
>>
>>
>>
>> 2 x ASR1001's (ASR1 and ASR2) directly connected (POPA), with OSPF, MPLS
>> and BGP established
>>
>>
>>
>> ASR1 connects to POPB (ME36001), also with OSPF, MPLS and BGP established
>>
>>
>>
>> ME36001 connects to ME36002 at POPB, also with OSPF, MPLS and BGP
>> established
>>
>>
>>
>> ME36002 connects to an ASR1006 at POPC, also with OSPF, MPLS and BGP
>> established
>>
>>
>>
>> We have a new link connecting to ASR2(POPA) that goes to POPD, also with
>> OSPF, MPLS and BGP established - but OSPF cost set high so that it is not
>> used...due to a strange outage it causes when OSPF is set to no cost.
>>
>>
>>
>> As soon as the new link on ASR2(POPA) and ASR1006(POPD) OSPF is set to no
>> cost, ASR2(POPA) for some reason establishes LDP to ME36002(POPC) - but it
>> has no direct connection to this device, nor is targetted LDP enabled to
>> this device, and ASR1(POPA) establishes LDP to ASR1006(POPC) - but it also
>> has no direct connection to this device, nor is targetted LDP enabled to
>> this device....result of these LDP sessions establishing is ASR1(POPA)
>> losing BGP neighbourships to three other routers that are connected via the
>> ASR1006(POPC).
>>
>>
>>
>> Ive opened a TAC case, but if anyone can explain how/why the LDP sessions
>> would establish when this new link is "activated" it would be greatly
>> appreciated!
>>
>>
>>
>> Cheers.
>> _______________________________________________
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>>
>
>
> Have you turned on remote-lfa under OSPF? This will dynamically create
> targeted LDP sessions.
>
> Regards,
>
> Dan loves willies


This is exactly what I was thinking. Are you using LFA/FRR, so these
are backup LSP?

Cheers,
James.


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