[c-nsp] MTU / BGP

[Adam Vitkovsky]

Hi,

Cmd: "ip tcp mss" affects TCP sessions only so BGP however also LDP sessions.

What does the log says is the reason for the session drop please?
If there's nothing obvious can you do "debug ip bgp x.x.x.x session" to see more details.
 

adam
> -----Original Message-----
> From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of
> CiscoNSP List
> Sent: 20 July 2015 08:02
> To: Mark Tinka; cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] MTU / BGP
> 
> 
> 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)
> 
> 
> ________________________________________
> 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,
> >
> >
> >
> > 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.
> >
> >
> >
> > 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)
> >
> >
> >
> > i.e. no neighbour xxx.xxx.xxx.xxx transport path-mtu-discovery on the
> ME's, I see
> >
> >
> >
> > Datagrams (max data segment is 9036 bytes):
> >
> >
> >
> > On the ASR RR's I see
> >
> >
> >
> > Datagrams (max data segment is 1940 bytes):
> >
> >
> >
> >
> > Any suggestions are greatly appreciated.
> 
> If you think it is MTU, configure "ip tcp mss" to something like 1000
> and test again.
> 
> Mark.
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