performance gain when dsl modem off
 

I am very encouraged by the immediate noticible boost in performance (ok responsiveness at least) of my workstation (fedora core 4) once I switch the DSL modem off - it speeds up to a degree which makes me wonder why it is so sluggish normally. any ideas on this? is there something about my router firewall or iptables firewall that I could set so I could get the same performance with the bandwidth "on" ? is there some more optimized networking driver that would help? the router has a built in 4 port Switch, and there is also another 4 port switch with practically NO traffic on a small lan between mostly dormant machines. thanks for any ideas...