Agreed, if a player wants to get back on a server, they will always find a way.
IMO banning IP address ranges or RDNS names is just stupid and overkill (in most situations), though under some circumstances I would not be against banning IP ranges or RDNS names of proxy/vpn providers that unsavory characters frequent. That would only be for certain providers of course, plus if a legitimate user wants to play the game bad enough, they can always use one of the many other providers out there (whereas the unwanted players ‘may’ give up after being forced to use a more expensive service, etc).
One other possible solution would be to monitor the server for login requests, check the login IP against a list of troublesome IP addresses and RDNS names, and then shoot an email over to the admins (only if an admin is not logged in at the time, to cut down on spam) notifying them of the login. The admin could then logon and make a decision of whether to ban or not based on their own discretion. This solution could quickly go south though if an admin has an itchy trigger finger.
You would of course have to identify the player under their new IP too, which could be a hassle if they are not obvious (though there are ways to narrow in on the players by using information gathered outside of the defcon server, but that is hit and miss).
It should not be forgotten that there is always the chance that multiple people are playing under the same IP (public libraries, hotspots, etc). Any time you ban an IP there is always a risk of banning innocent players, it should only be a last resort.
While I wouldn’t play defcon over my phone’s connection (lag/reconnection issues), phones are great for pestering people on IRC channels if they keep banning your IP
Can restart your phone and be back on the channel within a minute of being banned lol.
