Tutorial:Chunk ban
Use at your own risk.
Chunk banning[Java Edition only] is making a chunk or item contain too much data for servers to send to the client, resulting in repeated Java exceptions that disconnect users from the server that are in range. It is called a "ban" as the repeated Java exceptions prevent players from connecting to the server.
There are two methods of chunk banning; the first is the method of building high NBT structures, although this does not work in recent versions. The second (and more reliable) chunk banning method, now known as area banning, is to fill a shulker box with high NBT books and drop it as an item entity. Unlike chunk banning, this will kick you from the game if you are within a 32 block radius blocks of the dropped item on a server (this will increase to 48 if the user doesn't have a render distance of 2). In addition, if any entity such as a Fox or a Zombified Piglin holds a Shulker Box with high NBT books this will also act as a ban, often called a mob ban.
Area banning is not functional on Paper and Purpur server software, but works on vanilla servers and modded ones, such as Fabric.
Area bans are mainly used in prisons and also feature use in anarchy servers, and safe houses to keep people out of certain places. The first reference of a chunk ban was the furnace chunk ban in 2b2t, and the first non-anarchy reference was in a prison called The Obelisk by Miningblob. Ever since then all serious prisons as well as some safe houses have been made with area bans, most notably Gaia's Vault by TheDeafCreeper+SeenSven+JerryLum and Wifies' safe house.
There is a lot of misinformation about the difference between Chunk bans and Area bans; so watch this informative video by Jerrylum to fully understand Area Banning.
When in range of an area ban a player is still able to perform a few actions, due to players having a brief window of about a few ticks before the server kicks them from the game, this is called banned inputs
DO NOT hold it in your inventory if playing on 1.18.1 or higher. This will ban the player whenever they re-join the server in a method called inventory banning. The solutions are either to change the nbt data in the server/world file to remove the shulker box or to have a friend place a repeating command block with "/clear @p shulker_box" near you and then try to join, or if it is in a survival server a hole can be cleared going down into the void, and having the player fall into the void using banned inputs where they can die.
All area bans made before 1.21 will no longer work in 1.21, this is because the maximum packet size has been increased. Area bans can still be made post 1.21: this is done by adding more books to the shulker box using bundles, or by writing books that contain much more data displayed in this video by avatardotpng, this style is called compression banning.
There is a special type of area ban called a ZPI (Zone Protection Item). This ban works by containing a precise amount of data so that if loaded it will not be a sufficient amount of data for a kick. However, if placed into an item frame it will then be over the packet data size limit. This makes all players in the vicinity able to remain on the server, however, if new players load this area they are sent the packet for both the ZPI and the item frame which will kick them from the game. This type of ban was discovered by JerryLum.
Additionally, post 1.21 a ZPI can be active in a players' inventory. If a player holds the ZPI in their hand it will be act as a normal ZPI (They may also have to hold an item with multiple enchantments in the other hand), however this is a very risky thing to do, as this means that various gameplay functions (opening the inventory, equipping armour, using fireworks, etc.) will cause the player performing said actions to get kicked and become inventory banned.
If an area ban item is placed inside of a decorated pot, it creates a special type of area ban called a pot ban that bans a 7*7 chunk area (this is based on the client's render distance) centered around the chunk that contains the pot. This ban acts for a different reason than standard area bans and due to this, this ban is completely functional in singleplayer, and requires a much lower amount of data to function. Additionally, this type of ban will act as a ZPI and it was discovered by rzghuul. A more powerful version of this can be created by instead using a shelf, which will kick all players in the range instead of acting as a zpi, however if a lower data amount is entered it can still act as a zpi, shelfBans were discovered by StayedBoot7207 (shelfBans are currently the only ban type working on paper software but is likely to be patched soon)
As area banning works by having the server send oversized packets to users, any method of preventing packets from being sent to a client will prevent them from being kicked. The most common and most practical way to do this is by entering null state (this can be done by opening chat, then right clicking on the Minecraft window while in the chat bar.)
A void ban or void queue is a type of ban that consists of item frames with high data books, if enough of them are placed in the same chunk they can create a ban with a few unique interactions, this allows users to bypass areabans due to the game client failing to load new entities, after about 30 seconds the user will be kicked and re-joining has the same effect as re-joining into a standard areaban, this areaban has a unique range and more details can be found in this video explaining the type of ban and this video demonstrating how void queuing can bypass areabans
In Bedrock Edition, if a user attempts to create an area ban with enough data they may create a different and unique type of ban called a slot ban. This will kick a player if they hold the shulker in their hand with the message "An error has occurred". This may be possible to escape if the player switches the item in their hand as they log on, if the player has 9 slot bans in all hotbar slots they will be permanently banned from the game. If the shulker is too low data it will instead create a drop ban which will kick the player if they drop it from their hotbar.
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