>  > Could be TCP window scaling. See
>  > http://en.wikipedia.org/wiki/TCP_window_scale_option
>  > Or the plain old PMTUD problem described in
>  > 
> http://www.cisco.com/en/US/tech/tk870/tk877/tk880/technologies_tech_note09186a008011a218.shtml#backinfo
>  >
>  > =Adriaan=
> Nothing helps.
> I've tried to change client's mtu, even shrinked packets with ng_tcpmss 
> - no effect.
> I don't understand why freebsd machines from internal network can't 
> establish  any TCP connection to external net too.

Sounds to me like you need to carefully go over your network setup.  Have
you verified that the problem machines correctly have all the information
they need: proper netmasks, routers, etc?  Run tcpdump on both
interfaces of the gateway and see if that provides any hint.

I have a strong suspicion that you're looking in the wrong place --
otherwise you would have found the problem.  Are there two DHCP servers
on this network?  Wouldn't be the first time I saw that problem mess with
someone's head.

With the information you've provided so far, we're guessing in the dark.
I doubt that ipfw is the culprit, but it's going to take more information
to be sure.

> Can ipfw or netgraph detect client's OS type and allow only Windows XP ? =))

Potentially, but I can't see it doing that by accident.

Bill Moran
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