Let's say there's ANet.
If I run a server, and one of the ANet servers agrees to let me connect to it, everything I send over that S2S connection propagates to the whole ANet.
I'm part of ANet now.
If I then let Eris connect to my server, Eris becomes connected to ANet.
Now, if this was EFNet not ANet, that would violate the Eris-free invariant, so EFNet would need to apply secondary sanctions and disconnect from my server, in order to stay Eris-free.