Curious loss of bandwidth

From: Simon Gornall (simon@gornall.net)
Date: Fri Feb 07 2003 - 05:35:43 EST


Hi all,

I have a problem with my link to the Co-Lo facility that the internet
server is located at. The system is set up as

 +---------+ +------------+ Colt +--------------+
 |Local Lan|<--->|NAT firewall|<------>|Outer firewall|<--->...
 +---------+ +------------+ +--------------+
                                             A
                                             |
                                             V
                                           +---+
                                           |DMZ|
                                           +---+

With the problem appearing to be at the 'Colt' link stage. The link has
been tested by Colt, and verified to be running at a steady 100Mbps
without any errors, so I don't think it's the wire. The problem is that
it is only transferring about 200kbit/sec rather than 100Mbit/sec :-((

Transferring files from a DMZ machine to gatekeeper runs at approx
6MByte/sec. No problem there. The same story between the local lan, and
the NAT firewall (keymaster). But trying to transfer files from
keymaster to a DMZ machine (there's no FTP on gatekeeper) is *really*
slow.

There's no bandwidth shaping that I know of on the link, and I checked
using mii-diag that the link was working ok on both gatekeeper and
keymaster. Neither machine is logging errors on its' interfaces. The
load on either machine is really low (0.01 ranging to 0.04), and in fact
I can get 1Mbit/sec via my home ADSL connection from gatekeeper, so I
doubt it's the firewall that's causing the slowdown.

At this point, I'm stumped. The line is ok, the interfaces are ok, there
aren't any errors, and yet it's running at 1/50th the speed it should...
All the cards are intel etherexpress Pro's btw.

I'd be really grateful if anyone has any ideas ...

ATB,
        Simon

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