Ident

When a player connects to a MUSH game, this causes the game to initiate a query back to the player's machine on port 113. The ident protocol only works if the player's machine is running an ident daemon, and these days, most are not. The query requires that a connection between the two machines already exist.

A good introduction to the Ident protocol appears at http://en.wikipedia.org/wiki/Ident.