Ports
The officially assigned port numbers are 194 (”irc”), 529 (”irc-serv”), and 994 (”ircs”). However, these ports are in the privileged range (0-1024), which on a Unix-like system means that the daemon would have to have superuser privileges in order to open them. For various security reasons this is undesirable.
The common ports for an IRCd process are 6665 to 6669, with 6667 being the historical default. These ports can be opened by a non-superuser process, and they became widely used.