[c-nsp] Re: [MPLS-OPS]: MPLS LDP neighbouship Flapping

[Raju Raghavan]

The resolution to the problem is very valid.You must have to mtu in the core 
adjusted to have 1500 byte packets with the labels on travell across the 
core without fragmentation.

Regards
Raju Raghavan



----- Original Message ----- 
From: "Atiqur Rahman Mohammed" <atiqurrahman.mohammed at gmail.com>
To: "cisco-nsp" <cisco-nsp at puck.nether.net>; <mpls-ops at mplsrc.com>
Sent: Wednesday, November 16, 2005 8:26 PM
Subject: [MPLS-OPS]: MPLS LDP neighbouship Flapping


> Please find the resolution to issue. The problem is resolved  by TAC
> case .  Provide your comments.--
> Regards,
> Atiqur Rahman
> Infocomm Technology Cente
> Reliance Infocomm
> Mobile: 09324621784
>
>
> desakov at cisco.com
> 11/16/2005 07:58 PM
> To
> atiqurrahman.mohammed at relianceinfo.com
> cc
>
> Subject
> 602346373 Packet loss between two connected c7600 -  CT20051029_0000001364
>
>
> Hi Atiqur,
>
> The issue with LDP neighborship and EoMPLS VCs is caused
> by the fact, that 1500 bytes ip packets can not go from Loopback
> 192.168.71.165 to Loopback  192.168.71.161. As you said, only
> 1470 bytes packets can travel accross the "Core" network.
>
> I could see that TCP session (LDP uses TCP) between 192.168.71.165
> and 192.168.71.161 gets established, but when it comes to label
> advertisements, TCP keeps retransmitting the packets and eventually
> times out.
>
> So to make LDP working, we shall provide it with sufficient MTU.
> Now I configured 'ip mtu 1462' on the interface of "192.168.71.165" and
> this caused TCP to reduce it's packet size and now LDP session is
> stable and EoMPLS VCs are up.
>
> However, I do not think this is a solution, because user traffic in this
> EoMPLS VCs will be 1500 bytes of IP packet + ~18 bytes ethernet
> header + MPLS label. This will not work if the maxim packet you can
> send accross "Core" is 1470. You shall check with administrators
> of "Core" to fix the MTU issue. Normally, you shall be fine if you
> can send accross 1530 bytes MPLS packets.
>
> Please let me know if there are any questions or if there is anything
> else what I can do for you. Thanks!
> Dmitriy
>
> Cisco Technical Support Website: http://www.cisco.com/techsupport
> Cisco TAC Service Request Tool: 
> http://www.cisco.com/techsupport/servicerequest
> Cisco Technical Support Newsletter: 
> http://www.cisco.com/techsupport/newsletter
>
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