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Date:      Sun, 4 Feb 2001 21:34:15 -0500
From:      "Matthew Emmerton" <matt@gsicomp.on.ca>
To:        <freebsd-questions@FreeBSD.ORG>
Cc:        <freebsd-net@FreeBSD.ORG>
Subject:   Re: Firewalling a PPPoE, any easy workaround to MTU on lan  stations ?
Message-ID:  <004301c08f1c$22a8adb0$1200a8c0@gsicomp.on.ca>
References:  <000501c08ed2$2e1c5920$3227e540@johnny2k> <4.3.2.7.0.20010204201824.00bd33c0@mail.bsdchicks.com>

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> At 10:22 4-2-01 -0800, Julian Elischer wrote:
> >John Telford wrote:
> > >
> > > I'm putting  a 4.2 R firewall in for a ppoe connection. (sympatico)
> > > Is there any workaround I can use so I don't have to reduce the MTU on
all
> > > the internal stations ?
> > > It's a mix of Windows 9x and Macs. And I've found only one utility
capable
> > > of adjusting MTU on Macs.
> > > Can anything be done on the freebsd box as the traffic goes through it
?
> > > Thanks in advance, John.
> > > P.S. the pppoe setup went fine thanks to a page at
www.sympaticousers.org
> > > and some further notes at www.freebsddiary.org
> >
> >
> >ppp now has an option where it will force the negotiated packet size
> >of new tcp sessions going through it down. (i.e it fiddles with the
packets)
> >check the man page.. I THINK it may be in 4.2, if not it's in -Stable
>
> Actually, I have just been playing with this. Userland ppp has the 'set
> mtu' command which will make ppp try and set that MTU at negotiation time.

Isn't the proper command 'set tcpmssfixup'?  Sure, 'set mtu' will allow you
to set the MTU, but 'set tpmssfixup' will ensure that any MTU bashing
(explained very nicely at http://renaud.waldura.com/doc/freebsd-pppoe/) is
properly accounted for..

--
Matt Emmerton



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