[c-nsp] MPLS LDP neighbouship Flapping

[Atiqur Rahman Mohammed]

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
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