How does IRC's federation model compare to ActivityPub? July 3, 2021 on Drew DeVault's blog

Today’s federated revolution is led by ActivityPub, leading to the rise of services like Mastodon, PeerTube, PixelFed, and more. These new technologies have a particular approach to federation, which is coloring perceptions on what it actually means for a system to be federated at all. Today’s post will explain how Internet Relay Chat (IRC), a technology first introduced in the late 1980’s, does federation differently, and why.

As IRC has aged, many users today have only ever used a few networks, such as Liberachat (or Freenode, up until several weeks ago), which use a particular IRC model which does not, at first glance, appear to utilize federation. After all, everyone types “irc.libera.chat” into their client and they all end up on the same network and in the same namespace. However, this domain name is backed by a round-robin resolver which will connect you to any of several dozen servers, which are connected to each other1 and exchange messages on behalf of the users who reside on each. This is why we call them IRC networks — each is composed of a network of servers that work together.

But why can’t I send messages to users on OFTC from my Libera Chat session? Well, IRC networks are federated, but they are typically a closed federation, such that each network forms a discrete graph of servers, not interconnected with any of the others. In ActivityPub terms, imagine a version of Mastodon where, instead of automatically federating with new instances, server operators whitelisted each one, forming a closed graph of connected instances. Organize these servers under a single named entity (“Mastonet” or something), and the result is an “ActivityPub network” which operates in the same sense as a typical “IRC network”.

In contrast to Mastodon’s open federation, allowing any server to peer with any others without prior agreement between their operators, most IRC networks are closed. The network’s servers may have independent operators, but they operate together under a common agreement, rather than the laissez-faire approach typical of2 ActivityPub servers. The exact organizational and governance models vary, but many of these networks have discrete teams of staff which serve as moderators3, often unrelated to the people responsible for the servers. The social system can be designed independently of the technology.

Among IRC networks, there are degrees of openness. Libera Chat, the largest network, is run by a single governing organization, using servers donated by (and in the possession of) independent sponsors. Many smaller networks are be run on as few as one server, and some larger networks (particularly older ones) are run by many independent operators acting like more of a cooperative. EFnet, the oldest network, is run in this manner — you can even apply to become an operator yourself.

We can see from this that the idea of federation is flexible, allowing us to build a variety of social and operational structures. There’s no single right answer — approaches like IRC are able to balance many different benefits and drawbacks of their approach, such as balancing a reduced level of user mobility with a stronger approach to moderation and abuse reduction, while simultaneously enjoying the cost and scalability benefits of a federated design. Other federations, like Matrix, email, and Usenet, have their own set of tradeoffs. What unifies them is the ability to scale to a large size without expensive infrastructure, under the social models which best suit their users' needs, without a centralizing capital motive.


  1. Each server is not necessarily connected to each other server, by the way. Messages can be relayed from one server to another repeatedly to reach the intended destination. This provides IRC with a greater degree of scalability when compared to ActivityPub, where each server must communicate directly with the servers whose users it needs to reach. It also makes IRC more vulnerable to outages partitioning the network; we call these incidents “netsplits”. ↩︎

  2. Typical, but not universal. ↩︎

  3. There are two classes of moderators on IRC: oppers and ops. The former is responsible for the network, and mainly concerns themselves with matters of spam, user registration, settling disputes, and supporting ops. The ops are responsible for specific channels (spaces for discussion) and can define and enforce further rules at their discretion, within any limits imposed by the host network. ↩︎

⇒ This article is also available on gemini.

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