Port 8333 Bitcoin · TCP

What runs on port 8333

Bitcoin's peer-to-peer port. A full node accepts inbound connections here to serve blocks to other nodes; the JSON-RPC interface is on 8332 and must never be exposed. Testnet uses 18333, Lightning (LND) uses 9735.

Software that uses it: Bitcoin Core · btcd · Lightning nodes (9735)

Should port 8333 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.

• An inbound-reachable node helps the network; a reachable 8332 loses you your coins.

Check port 8333

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :8333'
sudo lsof -i :8333

# from another machine: is it reachable?
nc -zv host 8333
nmap -p 8333 host
curl -v telnet://host:8333      # 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 8333

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 8333 proto tcp
sudo ufw deny 8333/tcp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 tcp dport 8333 accept
nft add rule inet filter input tcp dport 8333 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 8333 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 8333 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=8333 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 8333" with no source is just "open".

Related ports

• 9735 Lightning Network
• 30303 Ethereum P2P

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