I have a 10Mbps ADSL2+ line.
When I connect my Linux box to the DSL modem directly I can get the expected speeds (10Mbps/512kbps).
When I let my DIR-600 make the DSL connection and my Linux box connected to the router using a wired connection (on wireless it's even worse) I get varying speeds between 0.5 and 4Mbps downstream, and 32kbps (yes, 32kbps) upstream.
The router is brand new, firmware upgraded to the latest version (2.03). My previous router was a WRT54G and never had this problem. Also, the line including the modem has been double checked by tech support, so it's now definitely the router...
Hints would be greatly appreciated.
+++ UPDATE +++
It was apparently a firmware issue. After giving it some thought I decided to replace the factory firmware with DD-WRT. And guess what. Speeds were immediately back to the expected values. No more performace problems. For those interested, I am using a DIR-600/B1 with DD-WRT v24-sp2 (04/23/10) std. It's beta at this time, but works flawlessly so far. I can only recommend it to all.