Port 6667 IRC · TCP

What runs on port 6667

The port IRC networks actually use for plaintext connections (194 is the registered one almost nobody uses). 6697 is IRC over TLS. Also historically a port used by IRC-based botnet command and control, which is why some corporate firewalls block it outright.

Software that uses it: InspIRCd, UnrealIRCd, ergo · Libera.Chat, OFTC (networks) · irssi, WeeChat, HexChat

Should port 6667 be open?

Designed to face the internet. This port exists to be reachable from anywhere, so the usual question is not whether to open it but how the service behind it is configured and patched.

• Connect on 6697 with TLS; most networks support SASL for authentication too.

Check port 6667

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :6667'
sudo lsof -i :6667

# from another machine: is it reachable?
nc -zv host 6667
nmap -p 6667 host
curl -v telnet://host:6667      # raw TCP connect test, Ctrl-C to leave

A port that answers from the internet when it should not is the finding; nmap from a machine outside your network (or a VPS) is the honest test, because scans from inside the LAN pass the firewall you are trying to verify.

Allow or block port 6667

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 6667 proto tcp
sudo ufw deny 6667/tcp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 tcp dport 6667 accept
nft add rule inet filter input tcp dport 6667 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 6667 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 6667 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=6667 protocol=tcp accept'

Replace 10.0.0.0/8 with the networks that need access. Allowing by source address is the rule that matters; "allow 6667" with no source is just "open".

Related ports

• 6697 IRC over TLS
• 194 IRC
• 113 ident

Part of the port number reference. Ports are 16-bit numbers; see also the subnet calculator and the packet decoder, which shows ports inside TCP and UDP headers.

Questions