Hi,

I struggled for a few months with this issue so thought i'd share the solution for anyone it may apply to.

Setup:
Draytek 2930VN
Windows client/server environment
(Windows 2003 DHCP server)

Problem.
Running with the draytek 2930VN to perform general router funtions, but disabled the DHCP function as i wanted my 2003 DHCP server to assign ipaddress. Enabled the DHCP relay funtion so the router would forward the DHCP requestes to the windows DHCP server.
This worked but i experienced very poor LAN and WAN (internet) performance, to the point it was barely working.

I tired all sorts of setup configs and permutations down the the most basic.

Resolution:
To cut a long story short, i enabled the routers DHCP funtion via the web interface, but enabled the DHCP relay function via telnet. Although this means 2 DHCP nodes, they both run in sync, the Draytek router will assign the ipaddress but relay the DHCP info to the window DHCP box - and i dont get the really slow permornance issues.
I can run with the windows DHCP box happy in the knowledge its a mirror of the draytek, the windows box still allows all the usual functions you may need. (for my setup anyway)
the DHCP can also still be controlled via the windows box, as long as the router is assigning the ipaddress in the same range. But i've not tired other subnet/ip mixtures.

Hopefully this may help...