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Date: Thu, 13 Jan 2005 12:02:52 -0500
From: Chuck Swiger <cswiger@mac.com>
Organization: The Courts of Chaos
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To: Kevin Oberman <oberman@es.net>
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cc: freebsd-net@freebsd.org
Subject: Re: IPv6 TCP transfers are hanging
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Kevin Oberman wrote:
> What I don't understand is how this is happening. tcp.mssdflt is set to
> 1400 bytes and tcp.v6mssdflt is only 1024. If PMTU discovery was
> working, this should not be a problem. If PMTU discovery is not used,
> the MSS defaults should keep the packets small enough to work over the
> tunnel.

Doesn't IPv6 require a minimum MTU of 1280 bytes?  Try setting the IPv6 TCP 
MSS to 1350 or so, bigger than IPv6 code requires, but small enough to fit 
into the ~1400+ byte MTU effectively available when you tunnel the traffic.

-- 
-Chuck