Well, I noticed one thing from the tcpdump files -- in the 1492 case, your machine is sending a FIN to www.ssh.com. In the 1484 case, of course no FIN is sent. However, if you look at the 1492 tcpdump you'll see connection establishment, a packet sent to www.ssh.com (an http request I assume), a retransmit of that packet a second later (implying that the first did not arrive), an ack for that packet from www.ssh.com, and a fin from your box, which is then acknowledged.
I don't know what's causing it, but it appears that the application
you're using is seeing something it doesn't like, and is closing its
socket. I don't know why the www.ssh.com side does not send its own
FIN -- it should (it may also not be getting to you).
I would look at a tcpdump of a successful connection to
www.freebsd.org with the 1492 config (you said in an earlier post
that this works). You could also run with a slightly smaller MTU and
declare victory :)
--eli
In reply to Rostislav Krasny <[EMAIL PROTECTED]> :
>
> --0-2081754345-1041105297=:86278
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> --- Eli Dart <[EMAIL PROTECTED]> wrote:
> >
> > In reply to Rostislav Krasny <[EMAIL PROTECTED]> :
> >
> > > Thank you for your trying to help me. Your version of ppp.conf is very
> > > similar to mine. I don't have LAN here, but only one box with FreeBSD
> > > connected to the outside world through my ADSL modem. So ' set nat' and
> > > ' set proxy' options are not required in my case. I don't use
> > > ' set ifaddr' option because default arguments of it are good for me.
> > >
> > > I think that the source of my problem isn't in ppp.conf probably,
> > > but somewhere in TCP. Nobody answered me how MTU == MRU == 1484 solves
> > > my problem. Maybe there is a bug in TCP when MTU and MRU have some
> > > unstandard value. When I use Win98SE in the same box and the same ADSL
> > > modem with RASPPPOE driver of PPPoE I have no troubles when the MTU is
> > > 1492 there. This is why I think the source of the problem is in TCP
> > > implementation of FreeBSD. ppp have some dial with TCP, so maybe the
> > > source of the problem is there but most likely not in ppp.conf
> >
> > Are you blocking ICMP for "security reasons?" If so, you can't do
> > path mtu discovery, and tcp will break if it needs a smaller mtu
> > (which it appears that you do).
>
> No, I'm not blocking ICMP. I have recently installed FreeBSD 4.7-RELEASE
> with custom kernel that is a little simplified version of GENERIC. There
> is no firewall enabled, yet. Look at CUST01 file in the attachments, this
> is the configuration of the kernel of my system. I also ran `tcpdump -n`
> and saved its output when I ran `links www.ssh.com` in other terminal.
> I did it two times, the first when MRU == MTU == 1492 and the second when
> it was 1484. Look at 1492.log and 1484.log files in the attachments.
>
> P.S. If one blocks ICMP why he have troubles when MTU == MRU == 1492 but
> don't have the troubles when MTU == MRU == 1484 ?
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