DI-524UP will become deadly slow when downloading torrents

Question

I have a DI-524UP router that shares internet to two notebooks at home via wireless and a desktop via wired collection. It will become barely available/pingable via wireless when I download torrents on a desktop computer. Even when I limit download speed to 20% or less of available bandwidth - it must be something else, not the speed that causes the issue. I've tried limiting number of active connections and stuff but it will still not cure.

Is there anything I can do about this?

Answer 1

(Right now this answer is diagnostic only: if the first part is accurate, I'm planning to edit this with a solution.)

It seems likely that the NAT table is filling up; the DI-524 only has about 8 MB of memory, so the NAT table is relatively small. Though torrenting is probably what's causing your problems, torrenting may actually just aggravate an underlying condition.

To check if torrenting is clogging the NAT table:

1. Get a baseline of NAT table entries.
Download http://<your router's IP address>/natlist.txt and save it as natlist-baseline.txt. This file will serve as a point of comparision later on.
2. Restart the router.
It's easier to test with a blank slate.
3. Connect two machines to the network - one with a wired connection, the other wirelessly.
4. Enable logging on the router.
Use the wired machine to log into the router's web administration interface at http://<your router's IP address>/. Go to Status -> Log -> Log Settings, and make sure that "Dropped Packets" is checked. Go back to Status -> Log and remove all the current log entries by clicking "Clear".
5. Stress the router until it's unresponsive to the wireless machine.
On the wireless machine, ping the router continuously, so it'll be obvious when the router is unresponsive. On the wired machine, find an active torrent that is likely to cause the router to seize up (an Ubuntu distribution works well) and begin torrenting. You can stop torrenting once the router is unresponsive.
6. Check the router's log.
Use the wired machine to log into the router's web administration interface. Go to Status -> Log and look through all the log entries. Any "Out of NAT buffer" messages indicate that the router is filling up its NAT table.
7. Get NAT table entries again.
Download http://<your router's IP address>/natlist.txt and save it as natlist-post-test.txt.
8. Restart the router (or wait about 15 min.) to clear the NAT table.

If you saw "Out of NAT buffer" messages in step 6, it's time to compare the two files you've downloaded. Otherwise, the NAT table probably isn't your issue — sorry.

The natlist-baseline.txt and natlist-post-test.txt files are plain-text dumps of the NAT table and some associated diagnostics. Right now we're just interested in measuring the ratio between a typical number of NAT entries (the baseline) and the maximum possible number of NAT entries (the post-test). In each file, find the line that looks like

 total entries = <some number>

and divide the number in the baseline file by the number in the post-test file. If the ratio is much above 0.5, torrenting might not be the only issue at hand.