RE: Important New Requirement for IPv4 Requests

[Justin Horstman <jhorstman () adknowledge com>]

Default MSS for most linux is 0, which causes the kernel to calculate it as the interface MTU-40bytes. You can either 
change the MTU on the interface or more specifically use the 'ip route <ipblock> dev <interface> advmss <new mss>' 
command to update it on a per route basis.

~J


-----Original Message-----
From: Robert E. Seastrom [mailto:rs () seastrom com] 
Sent: Thursday, April 30, 2009 7:12 AM
To: Randy Bush
Cc: nanog () nanog org
Subject: Re: Important New Requirement for IPv4 Requests


Randy Bush <randy () psg com> writes:

> mtu clue is also useful.  here on tokyo b-flets, and i would guess in
> many other ppoe environments, you need to tune or lose big-time.

But not difficult to beneficially MiM:

in pf:
scrub in on gre0 max-mss 1400
scrub out on gre0 max-mss 1400

in cisco-land:
ip tcp adjust-mss 1400

i'm sure the linux folks can offer up something similar...

-r