According to this answer, automatic bans are at a lower level than the account, i.e. bans are based on IP address.
There are two problems with this:
- There are many people who share IP addresses that can negatively affected as a side effect of the ban.
- Banning an IP doesn't really accomplish much of anything as far as preventing a person from continuing to post: it's not that hard to change your IP address, and you can always just switch computers or networks.
IP bans are ineffectual in stopping the activity of malignant people, and have collateral damage that can affect normal people. In short: don't ban IP addresses.
Instead, use account bans. They don't accomplish anything less than an IP ban, but they don't cause collateral damage.