Slow network

At work I have to use smb to access all kind of data: source directories, project files, internal data and such. I use smb4k as friendly smb browser and am very happy with it. Until tuesday: Saving a php file with some 1000 LOC took 5 seconds, extracting a 37MiB bz2 file felt as it would never end (but finally did after 20 minutes). Further, I wanted to share some 2GiB data with a colleague via ftp. We had 35kib/s transfer rate!

35 is very low when used to 10MiB/s, but this day I had no time to investigate. On wednesday, network felt even slower than the day before. (I've gotta say that http traffic was fast as ever). What could it be? I fired up etherape and got a shock - I had connections to 300+ machines! The thoughts I had can be best described with "Oh my, I am master of a bot net! On my unix machine!".

After examining the graph in detail I noticed that my laptop did not have this connections alone - I saw all the traffic in the network, including my boss's yahoo messenger traffic... All this although our company network is a switched network, and I had a switch in my room the laptop was behind.

Looking at the switch in my room I saw it was some dumb hub that forwards all packages to all computers connected to it. That was a first point, but still did not explain why the main HP switch did act as a hub. Now I got a switch from the server room, replaced the hub and etherape did show just the three connections that were really coming from my machine. smb was fast! ftp was fast! What a relief, being able to work normally again.

The HP switch is still a mystery for us; it might act as a hub because it is configured to put some ports in a virtual network. Although there is one idea that also could be true: Maybe the network cable in my room shares the same port as the black box of Germany's secret service BND that is probably somewhere in our server room...

Written by Christian Weiske.

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