Blocking IP address with port forwarding

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http://serverfault.com – I have a website setup behind a router, so the router has the external facing address and it will forward requests to the webserver inside the network. If there are X number of invalid login attempts, that IP address will be blocked from logging in. The problem is that because the site is being accessed through port forwarding, all requests show up as though they are coming from the router address, and thus the router address becomes the blocked IP. I'm not sure if this is a limitation of the router (linksys wrt160n) or if this a more general issue. Is there a way to handle this? (HowTos)