Das Werkstatt

now this is one of the strangest problems I've ever had:
(regarding networking/routing)

[PROBLEM]
The available connection should be symmetrical ~30KByte/sek up/down.

...but with an upload of less than 10kByte/sek, the pings to our nearest gateway went up from <10msek to >2500msek and more timeouts than godd ones!

[BUG HUNTING]

Since our line was not supposed to be congested (7kByte/sek), I called our ISP, asking them if they had any troubles with their lines lately.
He said no, but asked me to unplug the CAT5 cable from the modem - and whoops: the ping was down to <10msek again.
So he just said: The problem's on your LAN side, sir.

I had absolutely NO clue why, but now I had to verify what's happening:
- I reconnected the CAT5 to the modem > Ping went up again
- Disconnected the firewall from the LAN > Ping went down again
(so I guess it wasn't the firewall)

- Reconnected the Firewall to the LAN and started disconnecting EACH computer on the LAN > So I found out, that after disconnecting a certain computer, the pings went down again.

- This computer did nothing special, just uploading some files with ridicilous ~3kByte/sek. But when I stopped this upload, the pings were find (<10msek) again.

- Now I had to find out if it why this happend and where the problem could "really" come from: So I started a download from another PC.
>worked perfectly.

- Then I tried downloading the same file on the "suspicious" machine > worked perfectly, too.

- Trying to upload a ~800kByte file revealed that it was not machine dependant, but it simple was a problem with the upload.

[POSSIBLE SOLUTION]
I found out that this was only the case when doing an upload - downloads went fine (constant ~30kByte/sek) - no ping timeouts.

After I told this our cable-modem provider, he said: "oops. I think I just found the problem - there was a wrong filter-setting in your modem. I'll update it - please try again in 30-40 minutes"

After ~1hour things finally worked properly again!!