[c-nsp] BGP MSS=576 bytes

[Antonio Soares]

This is what i got with 12.2(18)SXF15a and "ip tcp path-mtu-discovery" enabled:

6500#sh ip bgp neighbors 1.1.1.1 | inc (path-mtu|max data)   
Datagrams (max data segment is 536 bytes):
6500#
6500#
6500#sh ip bgp neighbors 10.10.10.1 | inc (path-mtu|max data)
Datagrams (max data segment is 1460 bytes):
6500#

MSS=1460 for directly connected peerings and MSS=536 for non-directly connected peerings. Got the same behavior for iBGP and eBGP.

So basically it didn't work as i was expecting. It seems SXI puts some order here.


Regards,

Antonio Soares, CCIE #18473 (R&S)
amsoares at netcabo.pt

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Phil Mayers
Sent: domingo, 15 de Fevereiro de 2009 11:53
To: Antonio M. Soares
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] BGP MSS=576 bytes

Antonio M. Soares wrote:
> Hello group,
> 
> I have a 6500 running 122-18.SXF7 with lots of BGP peers and all of 
> the BGP sessions have negotiated a MSS of 536 bytes. Here's an

I think you need a newer IOS. Certainly under SXI I see:

ac-core#sh ip bgp neighbors  | inc path-mtu|max data seg
   Transport(tcp) path-mtu-discovery is enabled Datagrams (max data segment is 536 bytes):
   Transport(tcp) path-mtu-discovery is enabled Datagrams (max data segment is 1460 bytes):
   Transport(tcp) path-mtu-discovery is enabled Datagrams (max data segment is 9060 bytes):
   Transport(tcp) path-mtu-discovery is enabled Datagrams (max data segment is 536 bytes):

...depending on whether the neighbor is similarly equipped to be jumbo-framed and PMTU.
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