F17 after uptime about 9 hours internet lags

After uptime about 9 hours the websites downloading very long, some time not answer log time or no answer at all,
even local web lags (ntop 127.0.0.1:3000), but ping is good to all sites and download speed to.
When i reboot the computer all works fine, rebooting router has no effect, other computers connected to this router works fine.
When i disable network in network manager - the local site answers amidiatly.

excuse me for my english )