Port 1521 Oracle DB · TCP

What runs on port 1521

Oracle Database listener (TNS). Clients connect to the listener on 1521, name a service, and are handed to the database. The listener has its own security history (unauthenticated administration in old versions), and the protocol is unencrypted unless native encryption or TLS is configured. Internal only.

Software that uses it: Oracle Database · Oracle RAC · SQL*Plus, SQLcl, SQL Developer (clients)

Should port 1521 be open?

Private network or VPN only. Nothing good comes from this port being reachable from the internet. Keep it on an internal network, reach it over a VPN or an SSH tunnel, and firewall it from everything that does not need it.

• tnsping and lsnrctl status are the first checks; "ORA-12541: no listener" means the port is closed or the listener is down.

Check port 1521

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :1521'
sudo lsof -i :1521

# from another machine: is it reachable?
nc -zv host 1521
nmap -p 1521 host
curl -v telnet://host:1521      # 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 1521

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 1521 proto tcp
sudo ufw deny 1521/tcp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 tcp dport 1521 accept
nft add rule inet filter input tcp dport 1521 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 1521 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 1521 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=1521 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 1521" with no source is just "open".

Related ports

• 1433 MS SQL Server
• 5432 PostgreSQL
• 3306 MySQL / MariaDB

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