At my new job I requested a Linux machine (Ubuntu 8.10). On the second day I was embarrassed when I found out that my synaptic update downloads were causing the network (windows machines on a T1) to come to a crawl!

I know very little about networking and am at a loss as to how to troubleshoot this issue. I ran the tc wondershaper script as a temporary work-around, but I think that only throttles HTTP. I am going to need to transfer files via SSH/FTP as well.

Any help would be greatly appreciated. I'm going to have difficulty advocating Linux at my new company if I can't get past this issue.

Thanks.

I always found the 'apt-get update/apt-get dist-upgrade' sequence from the command line a little easier on network resources. Also, are you SURE that it is your Ubuntu machine hogging network resources and not some rogue Window machine?

Hi, Robert. Thanks for your reply.

Even SFTP downloads cause latency throughout the network. As soon as I do any significant downloading through any protocol, the pings on the other windows boxes go from ~80ms to 1500-8000ms. So I don't think it's from another machine. It's clearly the addition of the Ubuntu/Linux machine that is causing the problem.

If i'm not mistaken, a T1 has only a bandwidth of 1.5 Mbit/s ( symetrical ).

If anyone downloads stuff on the network, it will go to a crawl.

again, I might be totally mistaken here.

Thanks for your reply, vesperatus.

A 1.5 MB T1 is fine for a small network. The network hardware normally throttles machines doing significant downloading - and it was working fine for the ~50 windows machines that had been on the network up till this point. Something bizarre is happening and it is definitely related to the new Linux box.

You need to allocate bandwidth. Anyway an Ubuntu update will not be beyond a few hundred MBs.
Yours is a networking problem.

Allright then.

Let's say you transfer a file from your computer to another one on the network ? Does it have the same effect ? Then, if you transfer a file from a windows machine to yours ?

update

I think I may have figured this out! I think it has something to do with this new machine having a Gigabit ethernet card. I changed the MTU of my ethernet adapter to 500. I tested downloading the latest kernel with the default 1500, and the network came to a crawl again (>3 sec pings and timeouts). Then I changed the MTU to 500, removed the kernel, downloaded it again, and... voila! The network didn't feel a thing.

Still, I wonder why I had to do this? I thought 1500 was the 10/100 standard. So if I was sending 1500 byte packets, why would this cause the network hardware to freak out?

Hm... Anyway, now I'm running Fedora - guess I could go back to Ubuntu, but I think I'll try Fedora for a while.

It sounds like a fragmentation issue. Have you checked your exterior router's interfaces and see if there is a smaller MTU set. Also, you might want to check your DMZ routers/firewalls aswell.

The NIC should not be causing issues unless it is defective, but that is unlikely considering you are passing traffic properly. If you have a GigE NIC on a FE network, it will use the FE speeds (assuming it is set to Auto-Negotiate). Maybe check the switchport the Ubuntu machine is plugged into and see if it is set to Auto or 10/100 Full/Half duplex. Some NICs have issues with Auto while others can't handle hard-coded speeds.

I'm pretty sure it's a fragmentation issue though.