I keep needing to do this – so once again to help my future self:
When you have a number of public IPs being translated through a router to an internal address space, a router’s dynamic translation can get full. I’ve got an 877W, and it seems that a combination of running BitTorrent and a CounterStrike: Source server can quickly cripple the router (even with a memory upgrade!). When it gets too full you end up getting timeouts on other connections, usually this is most obvious by my browser failing to return pages.
To clear the dynamic translation table before timeout occurs log in to the router via ssh (or telnet) and in enable mode, type:
clear ip nat translation *
That seems to do the trick on my network anyway.