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

[Dan Peachey]

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