Okay, so I’m a moron. While it was an entertaining exercise, yesterday’s bit about using PHP to block IP addresses probably wasn’t completely necessary. Yes, that’s right – Movable Type has IP banning built right in. So I just add the IP address to the list, and the only functionality that changes is that the user cannot leave a comment, nor can they send a trackback. Geez…
If you haven’t used it, banning by IP can be remarkably useful. But it’s also potentially dangerous, because with the advent of NAT (network address translation), more than one user may be using that address you just banned.
This is especially prevalent at large ISPs such as AOL, and it’s really more of an issue because someone who is really determined to get at your site and leave you spam comments is typically quite adept at bypassing IP filtering by using open proxies, so the IP address they used a few seconds ago isn’t going to be the same one they use a few seconds from now. In other words, be careful when you use IP banning, as it may not help as much as you think it should.