6660-6669 IRC (alt range) TCP
Reference for TCP port 6660-6669, commonly associated with IRC (alt range).
What it's for
Ports 6660–6669 are the de facto standard range for IRC (Internet Relay Chat) servers — despite 194 being the officially IANA-registered IRC port, real-world IRC networks overwhelmingly run on this higher range instead, a convention that solidified decades ago and never really changed. Most IRC clients default to trying 6667 specifically when no port is given.
Protocol basics
Servers in this range speak the same IRC protocol regardless of which specific port within 6660–6669 they use — the range exists mainly so a server can offer several ports (sometimes with different ones behind firewalls that block others) rather than any of them having distinct protocol meaning. Traffic on these ports is plaintext by default; encrypted IRC ("IRC over TLS") typically runs on a separate dedicated port (commonly 6697) rather than anywhere in this range.