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From: Michael E.Conlen <meconlen@obfuscated.net>
Date: Fri, 28 Jan 2005 16:50:26 -0500
To: Chuck Swiger <cswiger@mac.com>
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cc: FreeBSD Mailing List <freebsd-questions@freebsd.org>
Subject: Re: pf and different MTUs
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On Jan 28, 2005, at 4:36 PM, Chuck Swiger wrote:

> Michael E.Conlen wrote:
>> I'm using FreeBSD and PF as a firewall between two  networks. I want 
>> to change the MTU on one network to 9k but I have to leave the MTU on 
>> the other network at 1500 bytes. Will the system handle the 
>> fragmenting for me going from the larger MTU to the smaller?
>
> Sure.  However, if you have a lot of traffic using jumbo frames going 
> over that 1500 MTU segment, you might be better off using an MTU of 
> 1500 everywhere.
>

At least half the traffic I use now doesn't go over that link and would 
benefit from the larger MTU. In addition I'm constrained on resources 
for those servers where as I can add additional firewalls without great 
expense. On the other side there is a good bit of traffic going over 
those links that would use jumbo frames but not all of it would. In 
addition the cost of using two separate networks for the traffic would 
be more than adding two more firewalls (based on the cost of doubling 
the number of ports) so I'm figuring this is the way to go.

Thanks.