Date: Sun, 05 Mar 2000 22:13:39 +0000 From: Brian Somers <brian@Awfulhak.org> To: Brian Somers <brian@Awfulhak.org> Cc: Dermot McNally <dermot@mcnally.de>, Dermot McNally <dermo@mcnally.de>, freebsd-net@FreeBSD.org, peter@FreeBSD.org, jkh@FreeBSD.org, joe@FreeBSD.org, brian@hak.lan.awfulhak.org, brian@hak.lan.awfulhak.org Subject: Re: NAT issues with ppp - a fix Message-ID: <200003052213.WAA07676@hak.lan.Awfulhak.org> In-Reply-To: Message from Brian Somers <brian@Awfulhak.org> of "Sun, 05 Mar 2000 03:49:23 GMT." <200003050349.DAA03010@hak.lan.Awfulhak.org>
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> > > At 02:18 04.03.2000 +0000, Brian Somers wrote:
> > > >Hi,
> > > >
> > > >Because of a recent change in the way I connect to the net
> > > >(PPPoUDPoPPPoISDN), I'm now seeing this problem !
> > > >
> > > >Can you try the attached patch ? I believe this fixes the problem !
> > >
> > > Bad news on my side - it doesn't appear to have helped. My test case:
> > > Before applying the patch, I cvsupped to today's current and rebuilt the
> > > world. Then I set the gateway box and a FreeBSD alpha box on my internal
> > > network back to an MTU of 1500. I connected to confirm that the problem was
> > > still there (it was).
> > >
> > > Then I applied the patch, rebuilt and installed ppp. Same test. Same
> > > problem - well, same symptoms anyway. My two tests were, using Lynx to
> > > connect to effectively any WWW site and using fetch to download a biggish
> > > file. Fetch determines the file size (which I don't recall it managing to
> > > do before), but doesn't actually get any further with the download. Lynx
> > > manages to look up the site to which I try to connect, but then hangs at
> > > the "waiting for response" stage.
> > >
> > > I can packet sniff this if you think it will help - my setup is slightly
> > > different to yours: PPPoE via a DSL "modem".
> >
> > Mine is even more tricky... I've been battling this for some time
> > now.
> >
> > I've actually got
> >
> > laptop <mtu 1500>-ethernet-<mtu 1500>gate<mtu 1466>-PPPoUDPoPPPoISDN-<mtu 1466> - PPPoISDN gateway - <mtu 1500> 'net - <mtu 1500> - PPPoUDP gateway - 'net
> >
> > The tricky bit is that I have to run the PPPoUDP link in MP mode using
> > a 1466 byte MRRU. This will make the IP layer fragment the traffic to
> > 1466 bytes, allowing ppp to pile a UDP/IP header of 28 bytes back on
> > the front (and to add the 2/4 byte MP header and 1/2 byte protocol
> > header) before sending out the UDP datagram.
> >
> > It's vital that the PPP/UDP/IP packet is no more than 1500 bytes as
> > it's going to pop up at my gateway and then must travel across the
> > 'net to the PPP/UDP gateway before it's unpacked and reassembled into
> > what was sent out originally.
> >
> > I *think* this should work now - assuming the fragmentation side of
> > things is functional. I haven't proven things yet though.
> >
> > I'll follow up....
> [.....]
>
> This works (with the previous patch), but requires an MRRU of
> 1338.... as there can be up to 128 bytes of options (is this right
> anyone ?).
>
> This means three things. First, I get to play with doing MP over two
> separate ISPs for real (soon). Second I get a compressed ISDN link
> with a static IP despite the transport being brought up and down with
> dynamic IP numbers :*P
>
> And third, your problem must be something specific to PPPoE as it
> looks like there are no NAT/fragmentation problems any more
> (otherwise my setup can't work).
>
> I guess I'm gonna have to try to set up a proper PPPoE environment
> here. I'll follow-up when I can.
Hmm, I take that back. I'm still having problems. The problems can
be circumvented with an MRU/MTU of 1000 and an MRRU of 1500 - causing
ppp to set the iface to 1500 and chop the results up into 1000 byte
frames.
This'll need more testing before I can even look at trying to
reproduce something consistently :-/
--
Brian <brian@Awfulhak.org> <brian@[uk.]FreeBSD.org>
<http://www.Awfulhak.org>; <brian@[uk.]OpenBSD.org>
Don't _EVER_ lose your sense of humour !
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