Banning a member

If a banned member's ISP assigns him/her a "dynamic" IP address, is it necessary to ban all IP addresses that user has used? And, what will prevent them from being able to create a new account when the ISP assigns him/her another dynamic IP address?

Thanks in advance.

If you ban the one of the Ip's it will ban the others. But the user can come back with a proxy IP. No way of stopping the proxy IP unless you keep banning them.

Proxy IP is slightly different from a Dynamic IP, correct?

Yes it is.