[c-nsp] BGP MSS=576 bytes

[Dale Shaw]

Hi,

2009/2/12 Antonio Soares <amsoares at netcabo.pt>:
> This seems buggy to me :(

Bad documentation, at least. The IOS 12.4 *mainline* command reference
and config guide waffle on and on about 'bgp transport' yet the
command (BGP router config mode or per-neighbour) doesn't even exist
in that train.

I suspect when it does exist (allegedly in 12.2(33)SRA, 12.2(31)SB,
and 12.2(33)SXH and 12.4(20)T), the behaviour is as described -- BGP
uses the BGP-specific TCP MSS settings. Without it, it uses the global
default (PMTUD off), and you need the 'ip tcp path-mtu-discovery'
global command to make it work.

I've tested it on IOS 12.4 mainline and even for directly connected
neighbours, MSS is 516 bytes. Once 'ip tcp path-mtu-discovery' is
switched on (on both peers), MSS is 1440 bytes.

cheers,
Dale