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Date: Thu, 22 Nov 2012 14:20:06 +0100
From: Ingo Flaschberger <if@xip.at>
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To: freebsd-net@freebsd.org
Subject: Re: Low Bandwidth on intercontinental connections
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Am 22.11.2012 13:38, schrieb Marc Peters:
> interesting, the MTU is way lower, than i expected. Through the VPN 
> tunnel, only 1322 bytes are possible without fragmentation. ScreenOS 
> adds 42 additional bytes per paket and the FreeBSD box is receiving 
> 1364 bytes, according to tcpdump. From the outside (only one Netscreen 
> on the way), 1472 is the maximum possible size to send pakets without 
> fragmentation (-D). Which MTU would you suggest to use? Shouldn't the 
> MTU discovery of FreeBSD handle this correct?

do you see fragmented tcp packets on the receiving site in tcpdump?

When you load the tcpdump data (tcpdump -s 1500 -w filename ...) into 
wireshark, you can graph the speed (bit/sec, packets/sec) and do some 
more tcp analysis.

Kind regards,
     Ingo Flaschberger