Hi all, I'm crossposting this to both the NZADSL & NZLUG mailing lists
in the hope that each can assist. Please reply on the appropriate list.

A couple of months ago I started experiencing some unusual problems with
IRC Fserv'ing. (DCC Fserv's/Chat's). I've finally isolated this somewhat
to the MTU.

Essentials: Dedicated router running two internet connections, 1x cable,
1x dsl. The DSL is pptp linked to an Alcatel Speedtouch allowing a
realworld IP address on the router.
Scenario: DSL is the default route. Cable is selectively routed
depending on traffic type (ie: websurfing).
Problem: If DSL is shut down DCC operates normally through cable. If DSL
is online, IRC Fserv/DCC functions encounter problems. The DCC
connection is established, and the first line of the welcomefile is
displayed, but nothing further. This is exhibited under ip
masquerading, port forwarding, or socks5 proxying. All 3 exhibit
identical symptoms. If the connection is left for long enough other
lines will slowly appear before it times out.

Now that I've started playing with the MTU with MTU value 1200 things
are relatively reliable, however file transfer speeds are extremely
poor. I can push the MTU value higher, but stability and reliability of
fserv connections appears to go down. The highest I can get is about
1300 with some reliability.

I've read back through as many of the articles on the NZADSL mailing
list that deal with MTU values as I can, and there are several specific
mentions of dropping the MTU value to 1492 when dealing with pptp
connections. Historically I haven't needed to modify the MTU, and
although I expect matching the Windows MTU to the ppp (/pptp) value will
help with throughput it'd be nice to find a better solution.

Has anyone experienced any similar problems lately that sound along thes
lines? Also does anyone know if the MTU values in the network have been
altered at all? I'm aware that reverse_path filtering was turned on
several months ago thanks to a couple of replies for another problem I
had, but I don't know if MTU's were tweaked at the same time.
Alternatively does anyone have any other suggestions for to try?

The router is a RH9 based system running the following:
openmosix-kernel-2.4.22-openmosix2
ppp-2.4.2_cvs_20030610-1
pptp-linux-1.3.1-1

PS: I was just about to post this, and saw mention a post with mention
of 'new traffic queuing hardware' on DSL? Does anyone have any further
information?

Thx.
Jp.

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