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

Thu Sep 24 08:52:50 EDT 2015

Hi Michael,

Yeah it's been a while :) I'm doing good, enjoying my new job.
And how are you, I envy you the upcoming Summer :)

I'm wondering whether you have some VLAN interfaces that are configured as MPLS interfaces on the MEs.
There's this bug where if VLAN interface/mpls link is computed as LFA backup link then forwarding on the ME box is disrupted.
That could explain the BGP sessions but that would affect other traffic going through the box.

Also if you could perform mpls ping over the new link does it work please?

adam
>

        Adam Vitkovsky
        IP Engineer

T:      0333 006 5936
E:      Adam.Vitkovsky at gamma.co.uk
W:      www.gamma.co.uk

This is an email from Gamma Telecom Ltd, trading as “Gamma”. The contents of this email are confidential to the ordinary user of the email address to which it was addressed. This email is not intended to create any legal relationship. No one else may place any reliance upon it, or copy or forward all or any of it in any form (unless otherwise notified). If you receive this email in error, please accept our apologies, we would be obliged if you would telephone our postmaster on +44 (0) 808 178 9652 or email postmaster at gamma.co.uk

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-----Original Message-----
> From: CiscoNSP List [mailto:CiscoNSP_list at hotmail.com]
> Sent: Wednesday, September 23, 2015 10:28 AM
> To: Adam Vitkovsky; cisco-nsp at puck.nether.net
> Subject: Re: LDP sessions established to non directly connected routers,
> when new link is activated
>
> Hi Adam - Long time no speak...how have you been?
>
> Yes - Checked all routers, no tLDP sessions configured(To the routers the
> "new" LDP sessions establish), we have xconnects from the ME3600's in
> POPB -> ME3600's in POPA, but none from POPA -> POPC ASR1006 - And as
> you mention, they would come come up over the existing path, but only
> come up when this new link is activated.
>
> Once BGP fails to the three routers(Which is almost immediately after the
> "new" LDP sessions establish), it stays down, and only recovers once I re-
> apply the high OSPF cost to the new link...mtu's are definitely different(As
> we purchase them from different carriers)....but as soon as the LDP sessions
> establish, I am not even able to ping the routers that lose BGP.
>
> POPC(ASR1006) -> POPB (ME3600) mtu 1552
> POPB(ME3600)->POPA(ASR1001) mtu 3000
> POPA(ASR1001-2) -> POPD(ASR1006) mtu 1950
>
>
> Very strange one indeed :)
>
>
>
> ________________________________________
> From: Adam Vitkovsky <Adam.Vitkovsky at gamma.co.uk>
> Sent: Wednesday, 23 September 2015 6:11 PM
> To: CiscoNSP List; cisco-nsp at puck.nether.net
> Subject: RE: LDP sessions established to non directly connected routers,
> when new link is activated
>
> Hi,
>
> Have you checked both ends if either end has a tLDP session configured it
> would come up.
> Also xconnects are using targeted LDP sessions, isn't there some forgotten
> xconnect pointing to these routers somewhere?
> But then the question is why the session wouldn't be formed over the
> existing path.
>
> With regards to BGP failing are the sessions then re-established or they
> remain down please?
> I suspect it could be an MTU problem that is some of the links on the new
> path ASR2(POPA) to ASR1(POPD) to ASR1(POPC) -have lower MTU than the
> links on the existing path via POPB.
>
>
> adam
> >
>
>         Adam Vitkovsky
>         IP Engineer
>
> T:      0333 006 5936
> E:      Adam.Vitkovsky at gamma.co.uk
> W:      www.gamma.co.uk
>
> This is an email from Gamma Telecom Ltd, trading as “Gamma”. The contents
> of this email are confidential to the ordinary user of the email address to
> which it was addressed. This email is not intended to create any legal
> relationship. No one else may place any reliance upon it, or copy or forward
> all or any of it in any form (unless otherwise notified). If you receive this
> email in error, please accept our apologies, we would be obliged if you would
> telephone our postmaster on +44 (0) 808 178 9652 or email
> postmaster at gamma.co.uk
>
> Gamma Telecom Limited, a company incorporated in England and Wales,
> with limited liability, with registered number 04340834, and whose registered
> office is at 5 Fleet Place London EC4M 7RD and whose principal place of
> business is at Kings House, Kings Road West, Newbury, Berkshire, RG14 5BY.
>
>
> -----Original Message-----
> > From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf
> > Of CiscoNSP List
> > Sent: 22 September 2015 23:59
> > To: cisco-nsp at puck.nether.net
> > Subject: [c-nsp] LDP sessions established to non directly connected
> > routers, when new link is activated
> >
> > 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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