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

[Dan Peachey]

On 25 September 2015 at 02:57, CiscoNSP List <CiscoNSP_list at hotmail.com>
wrote:
>>
>>
> > Have you turned on remote-lfa under OSPF? This will dynamically create
targeted LDP sessions.
> >
> > Regards,
> >
> > Dan
>
> Hi Dan,
>
> Thanks - Yes we do:
>
> fast-reroute per-prefix remote-lfa area 0 tunnel mpls-ldp
>
> Guess my next question is, why wouldnt the LDP sessions establish with
this new link "not in use" ? (i.e. only occurs when we disable ospf cost?)
>
> Cheers.

What do you mean by "disable ospf cost"? A link will always have a cost. If
you mean you just aren't setting it manually, then it will be figured out
automatically (depending on interface speed, auto-cost reference-bandwidth
etc..).

Sounds like you have a ring topology and tLDP session is establishing as a
rLFA backup route due to equal cost paths.

I don't think the LDP session is causing your issue as it's a backup LSP.
Probably the issue is that you are pushing traffic via your new link and
for some reason it's breaking stuff. MTU mismatching would be my initial
thought. Make sure you have all your interface MTU's set correctly to match
the underlying circuit, also that you have 'ip tcp path-mtu-discovery'
configured and that you *don't* have 'no ip unreachables' configured on
your interfaces.

Cheers,

Dan