I have 2pc connected to router.1 is for torrent download.But even though I forwarded ports.Download is much slower than without a router.(Forwarded ports------6880~6889TCP.4444UDP4445UDP.50000TCP.4000TCP).

Try disabling DHT, maybe cut down on the number of connections (say only 30 per torrent)

Also, try not to use the default 6880-6889 range.

I am downloading much better,thanks.But I do not know about DHT settings,with my Buffalo router,BBR-4MG.It just don,have any setting exept TCP/UDP.

Try disabling DHT in your KTorrent settings. A lot of routers get overwhelmed by the amount of UDP communications DHT performs.

DHT was off,but still without the router is much faster.So I am downloading without.
Can I download as fast as without?If configuration is correct?

For beeing simple some router are cheap and not expensive.

But they make reduction cost on how much parallel connexion router can handle.

For a web usage you are using 10-30connexion maximum (3http,2imp,mail,rss,etc)

Bug in p2p software you make lot of connexion, each cost a small amount of bandwith and bandwith for dl and upload.

For example i have a stupid french isp box (neufbox trio3d) which handle maximum 200connexion in parallel.

If i set ktorrent general limit to more than 150connexion, i can't use website browsing (and whole net is unresponsive).
If i set ktorrent upload bandwith to more than 70KB/s (over 100KB/s in theory), same result.

So i suggest you to try look empiricaly how many parallel connexion your router can handle, and how many bandwith too.

My connexion is a 8Mb/800Kb adsl connexion.

Notice i didn't had such limits when i used pppoe connexion under my linux, but that's an other problem...

Well,I have started to use the router again(actually it is the cheapest model I have found).Because I 've found very basic mistake that I made a mistake in IP address for the port forward program.Because Wan port was 1 and router port 1 was 2,which I set to 1.Well stupid but I never have had a router before..... So ,now it's working ok.Downloading Mandriva 2007.1
about 40kb/s.About the same as without.