[c-nsp] MTU / BGP

[CiscoNSP List]

Thanks Mark - I have existing OSPF/MPLS/BGP sessions running over the links (Apart from the "new" ME's to the "old" RR's) - Adjusting MTU on the new ME's(Only), will it break any of those existing sessions? (As OSPF is very particular about MTU)


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From: Mark Tinka <mark.tinka at seacom.mu>
Sent: Monday, 20 July 2015 4:56 PM
To: CiscoNSP List; cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] MTU / BGP

On 20/Jul/15 08:47, CiscoNSP List wrote:
> Hi Everyone,
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> Have a new POP, 2 x ASR1000's (Acting as RR's), and 2 x ME3600's - We have another POP with 2 x ASR1000's also acting as RR's.
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> The 2 "new" ME's are peered to the "new" ASR's RR's, but if I try to establish BGP  session with the existing RR's, session establishes, but then drops on both ME's after ~4minutes...I *think* it's due to MTU, and have tried disabling path mtu discovery, but it doesnt appear to do anything? (also tried it with it enabled, and the results are the same)
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> i.e. no neighbour xxx.xxx.xxx.xxx transport path-mtu-discovery on the ME's, I see
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> Datagrams (max data segment is 9036 bytes):
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> On the ASR RR's I see
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> Datagrams (max data segment is 1940 bytes):
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> Any suggestions are greatly appreciated.

If you think it is MTU, configure "ip tcp mss" to something like 1000
and test again.

Mark.