ng_pptpgre problems: tcp connections reset unexpectedly

[Alexander Motin]

Hi.

Nikos Vassiliadis wrote:
>  It seems that tcp connections over pptp reset unexpectedly. I have
> tried several things such as connecting from a FBSD-4 to a FBSD-6,
> connecting from a FBSD-[46] to a Cisco router(*). There are times which
> the client box gets from the other peer an echo-request msg, which is
> not supposed to happen while downloading. Perhaps it's relevant to
> this:
> 
> (*) the result is always the same.
> 
> What i have not tried, is a newer mpd, Alexander Motin seems to
> maintain mpd very actively, he sends a patch every 5 minutes or so:)
> I am using at the moment 6.2-PRE, just a  few days before RELEASE,
> and mpd-3.18_4.

Actually I have spent so much time working on mpd4 that I dont like to 
even hear about some problems in ancient mpd3. :) There so much work was 
done in mpd4 that it is mostly pointless to debug something in mpd3.

> Could you please help? any workarounds, tunables, suggestions?
> It's my connection to the internet and from time to time I need
> to download something bigger than a few megs...

I do not use pptp actively, to say for sure, but you can try to play 
with such pptp options like delayed-ack, always-ack and windowing.

> Thanks in advance, Nikos
> 
> root:2:~/tst1# fetch ftp://ftp2.de.freebsd.org/pub/FreeBSD/ISO-IMAGES-i386/6.2/6.2-RELEASE-i386-disc1.iso; date 
> 6.2-RELEASE-i386-disc1.iso                      3% of  573 MB  185 kBps 50m56s
> fetch: transfer timed out
> fetch: 6.2-RELEASE-i386-disc1.iso appears to be truncated: 20702208/601229312 bytes
> Fri Jan 26 11:31:40 EET 2007

> tcpdump.ng0:
> 11:31:40.797285 IP 134.76.12.3.56123 > 213.142.137.253.64016: . 20695333:20696745(1412) ack 1 win 5792 <nop,nop,timestamp 50979088 694225824>
> 11:31:40.797294 IP 213.142.137.253.64016 > 134.76.12.3.56123: . ack 20696745 win 32476 <nop,nop,timestamp 694225916 50979088>
> 11:31:40.797697 IP 134.76.12.3.56123 > 213.142.137.253.64016: . 20696745:20698157(1412) ack 1 win 5792 <nop,nop,timestamp 50979088 694225824>
> 11:31:40.797780 IP 213.142.137.253.64016 > 134.76.12.3.56123: . ack 20698157 win 33182 <nop,nop,timestamp 694225916 50979088>
> 11:31:40.798589 IP 134.76.12.3.56123 > 213.142.137.253.64016: . 20698157:20699569(1412) ack 1 win 5792 <nop,nop,timestamp 50979089 694225826>
> 11:31:40.798739 IP 134.76.12.3.56123 > 213.142.137.253.64016: . 20699569:20700981(1412) ack 1 win 5792 <nop,nop,timestamp 50979089 694225826>
> 11:31:40.798748 IP 213.142.137.253.64016 > 134.76.12.3.56123: . ack 20700981 win 32476 <nop,nop,timestamp 694225917 50979089>
> 11:31:40.798877 IP 134.76.12.3.56123 > 213.142.137.253.64016: . 20700981:20702393(1412) ack 1 win 5792 <nop,nop,timestamp 50979089 694225826>
> 11:31:40.798924 IP 213.142.137.253.64016 > 134.76.12.3.56123: . ack 20702393 win 33182 <nop,nop,timestamp 694225917 50979089>
> 11:31:40.859025 IP 213.142.137.253.64016 > 134.76.12.3.56123: R 1:1(0) ack 20702393 win 33182
> 11:31:40.887739 IP 134.76.12.3.56123 > 213.142.137.253.64016: . 20702393:20703805(1412) ack 1 win 5792 <nop,nop,timestamp 50979098 694225914>
> 11:31:40.887859 IP 134.76.12.3.56123 > 213.142.137.253.64016: P 20703805:20705217(1412) ack 1 win 5792 <nop,nop,timestamp 50979098 694225914>
> 11:31:40.888005 IP 134.76.12.3.56123 > 213.142.137.253.64016: . 20705217:20706629(1412) ack 1 win 5792 <nop,nop,timestamp 50979098 694225914>

Looking here I can see that it is your local machine (213.142.137.253) 
sent "R" - Reset request just after normal acknowledge packet. I don't 
see the reason for such it's behaviour. Is it the same machine where 
fetch and tcpdump running? Wasn't there some kind of time 
synchronization or NAT restart or some other external event?

-- 
Alexander Motin mav at alkar.net
Optima Telecom