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 From:  "Chris Buechler" <cbuechler at gmail dot com>
 Cc:  m0n0wall at lists dot m0n0 dot ch
 Subject:  Re: [m0n0wall] Vista/MTU Problem - bug in traffic shaper
 Date:  Tue, 8 Apr 2008 21:15:24 -0400
On Tue, Apr 8, 2008 at 8:50 PM, Søren Vanggaard Jensen
<svanggaard at hotmail dot com> wrote:
> The Vista/MTU problems seems to keep haunting me.
>  I've seen several problems with Windows Vista and monowall. The problem is
>  probably caused by a default MTU setting of 1500 in the Windows Vista
>  network Layer.

No, every version of Windows is 1500 on Ethernet out of the box,
always has been.

>  If i edit the Vista registry settings (reduce mtu to
>  something < 1400) connectivity is restored.
>  In general i see the problems when the Vista is connected to
>  monowall/internet through a wirellesss router. Cabled connections always
>  works. Sometimes i've been able to correct the problem by setting MTU=1400
>  on WAN and OPT1 interfaces. However when I'm also using the captive portal i
>  the problems gets worse. In some cases the Vista client cannot even display
>  the captive portal loginpage.
>  I've recently discovered, that disabling captive portal bandwith limitation
>  solves the problem. That is, CP "per-user bandwidth restriction" has some
>  sort of bug.
>  Any thoughts?

First thing I'd suggest is trying the latest 1.3 if you're using 1.2.
My first guess is it's related to window scaling or other network
changes in Vista that brings up bugs in parts of ipfw and/or dummynet
in FreeBSD 4.x, which isn't surprising since it's been 5+ years since
any significant development has happened in 4.x and those type of
network changes didn't exist in widespread use at that point.
Adjusting the MTU apparently adjusts how the problematic portion
works, and avoids the issue. It's likely long since fixed in newer
FreeBSD versions.  If not, any troubleshooting efforts will need to
start with a newer FreeBSD version anyway to get anywhere.