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Date: Sun, 29 Aug 2004 20:43:44 -0700
From: Avleen Vig <lists-freebsd@silverwraith.com>
To: Dennis George <easyeinfo@yahoo.com>
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cc: freebsd-hackers@freebsd.org
Subject: Re: Finding MTU
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On Sun, Aug 29, 2004 at 07:55:27PM -0700, Dennis George wrote:
> Hi all,
>  
> Can anybody tell me how to find the MTU (Maximum Transmitting Unit) in
> freeBSD programatically...

Define programatically?
With syscalls, or in a way that is easily repeatable?

If you just mean the latter, this will do it:
  ifconfig -a | awk '/mtu/ { print $1, $NF }'

Otherwise, try  man networking  and look for the word 'mtu', that might
be a good start.