FTP over PPP stalls out

2boxers_at_comcast_dot_net
Date: 11/14/03 

Date: Fri, 14 Nov 2003 11:48:41 -0500

Maybe somebody else has experienced similar problems and can make
suggestions that pertain to what is happening to me.

I was running Mandrake 9. The system basically performed flawlessly.
I was able to PPP with a modem from the linux box, ftp over that
connection, as well as set up the linux box to be an IPTABLES NAT so
that workstations on the network could have Internet connectivity as
well. The modem line was a backup to the Cable Modem interface, which
also worked well under Mandrake.

I recently installed RH9 on this pc. I did this because I bought a
new RAID5 controller (S150SX4) from promise and it has specific kernel
requirements- one of them being 2.4.20-8 or 2.4.20-8smp. The
controller card is working fine and performance is acceptable.

Here is the problem:
PPP is performing poorly. There are 10 - 20% RX errors as well as 10
- 20% packet loss with simple pings.

This very same modem and phoneline when plugged into a system running
Windows XP performs fine.

This very same modem and phoneline also performed fine with the
previous Mandrake configuration .

Regardless of connect speeds which are either 28800 or 49333,
depending on whether or not I enable V90, I get 1.4 - 1.6KB/sec avg
speed over FTP. Note: this is a USR Courier V.everything modem.

I used to get over 4k on average with bursts of 5-6KB/sec.

With the packet loss and RX errors, needless to say, this PPP
interface is worthless as a NAT.

Here is my system:
Dual P2 400's. (Not a powerhouse, but it has been reliable for a
couple years now)
1GB pc-133 RAM
400GB RAID5
Intel Gigabit Ethernet
3Com 10/100 Ethernet
Adaptec 2940 w/Tandberg SLR5 tapedrive and NEC Cd-Rom
Panasonic IDE Cd-Rom
USR Courier v.everything modem

RH9
kernel-2.4.20-8smp
iptables v1.2.7a

So far I have tried:
connecting to a different ISP
using a different modem
lowering baud rates and line speeds
verified correct modem init string
asyncmap 0

None of this made much of a difference if at all.

During FTP transfers, both CPUs are virtually idle. 2-3% intermittent
utilization and yet the ftp performance is poor.

I tried using mru 576 and mtu 576 and there was a slight throughput
improvement. 1.9KB/sec, but nothing great. Packet loss and RX errors
still were at 10-20%.

Also, with mru and mtu at 576, workstations fail to transfer through
the NAT. It seems that the minimum that works over the NAT is 1500.

Can somebody suggest some things to test to help narrow down this
problem?

Thanks in advance,
Charles

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