There are two ways for Fediverse servers to communicate with each other, blocklists and allowlists:
- Blocklists are by far the more common option, and mean your server will connect with any other server that isn’t on your server’s blocklist. Your server can make connections with other servers more easily, but will be more at risk of receiving abusive posts from nasty servers that haven’t been added to its blocklist yet.
- Allowlists are less common, but many people prefer them due to their greater safety. If your server uses allowlists, all other servers are blocked by default and are only unblocked if they’re added to an “allowlist” by your server’s admin. Allowlists prevent the danger of rogue servers posting abuse, but they also make it harder to make connections with nice servers that haven’t been added to the allowlist yet.
By default Mastodon servers use blocklists. However, there is an optional setting on Mastodon called “Limited Federation Mode” where the server uses allowlists instead.
It is up to the admin of each Mastodon server to decide whether blocklists or allowlists are right for their particular server. Only server admins can adjust this setting.
I am a Mastodon server admin. How do I find out more about Limited Federation Mode?
If you’re an admin and want to find out more, there is a web page with instructions and tips on Limited Federation mode here ⧉ and there’s a technical description of Limited Federation mode ⧉ in the official documentation.
Allowlists vs Blocklists: How do they differ?
In default mode, Mastodon servers can communicate with other servers unless the server admin blocks them. This is known as a “blocklist” system, because it depends on the admin telling their server which other servers to block.
If a server runs in Limited Federation Mode, it’s the opposite way around: no other servers can communicate with the admin’s server unless the server admin specifically allows them. This is known as an “allowlist” system, because it depends on the admin telling their server which other servers to allow connections with.
Blocklists are better for building up connections with other servers, but worse for user safety. Allowlists are better for user safety, but worse for building up connections with other servers.
There may also be compatibility issues when using some apps with servers in Limited Federation Mode, because this is currently a rarely used setting that the app may not have been tested with.
How do I set my server to Limited Federation mode?
You need to be a server admin to change your server’s federation.
If a server is on a managed hosting company, the server’s admin will need to ask their hosting company to switch the server over to Limited Federation mode.
If the server has been set up manually by its admin, the server admin will need to make the adjustments manually by consulting the official Mastodon documentation on federation ⧉.
Will the apps work with a server in Limited Federation mode?
The server’s website and the web apps should work fine.
There may be problems with some app store apps working with servers in Limited Federation Mode. You might want to have a look at the guide linked to above ⧉ for more info on which apps work.
Can admins set their server to be totally isolated and not communicate with anyone?
Yes. If an admin sets a server to Limited Federation Mode and leaves the allowlist blank, the server will be totally isolated and have no connections with any other server.