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

[Dan Peachey]

On 25 September 2015 at 11:45, CiscoNSP List <CiscoNSP_list at hotmail.com>
wrote:

>
> >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 - New link currently has a manually set hight ospf cost, so it
> isnt "used"...by disabling cost, I mean removing the "ip ospf cost foo" on
> each Int of the new link.
>
> MTU on the new link is set identically at both ends, and can ping at that
> MTU...OSPF+MPLS established...although, Ive just found out that I cant
> "mpls ping" in one direction on the new link(Even though logs say its'
> established, and sh mpls ldp nei shows the neighbourship on the new circuit
> as "up"....so more investigations needed.
>
> Got a TAC case open, and have a maintenance window/webex with them in
> ~12hours...so hopefully we can get some debug info to find the underlying
> cause.
>
> Cheers for all the replies.
>
>
>
Ah, I didn't read "I am not even able to ping the routers that lose BGP", I
thought you were just having BGP establishment issues with that link up.
Let us know what Cisco come back with, could be a bug as others have
suggested.

Cheers,

Dan