Port 563 NNTPS · TCP

What runs on port 563

NNTPS: NNTP over TLS. What Usenet providers actually use today.

Software that uses it: INN · commercial Usenet providers

Should port 563 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.

• Most providers require it; port 119 is for local servers only.

Check port 563

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :563'
sudo lsof -i :563

# from another machine: is it reachable?
nc -zv host 563
nmap -p 563 host
curl -v telnet://host:563      # 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 563

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 563 proto tcp
sudo ufw deny 563/tcp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 tcp dport 563 accept
nft add rule inet filter input tcp dport 563 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 563 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 563 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=563 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 563" with no source is just "open".

Related ports

• 119 NNTP — Usenet news

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