IP Bans block a player's IP from accessing Assault Cube servers. When a player is IP banned, any device that is connected to their router (share the same IP address) will be banned from assault cube servers. IP bans are issued when a player has violated assault cubes rules like cheating. Most IP bans last for 3 months but some of them are permanent.
Even though Assault Cube officially states that IP Bans will block your access to any server, it has been observed that it only blocks your access to the master server list. If you know the IP of the server you are still able to connect to it using the custom connect option. You can see if you are IP Banned by requesting to see the master server list using this link:
Server Admins are able to view your IP Address except for the last row of numbers, this way they can blacklist your IP and also report you to the official Assault cube administrators.
IP Range bans
Public IPs are dynamic, meaning they change when you restart your router, restarting your router is enough to bypass an IP Ban. To combat this, Assault Cube doesn't just ban your current IP but also the range of /24 IP Addresses making it hard to bypass IP bans just by restarting the router. IP range bans are uncommon in most games because they can ban innocent players; Assault Cube however is willing to take this risk.
VPN subnets are automatically Banned from accessing the master server list.