Port 9042 (Apache Cassandra CQL)

Cassandra and ScyllaDB native CQL client port.

Registered (user) port, 1024-49151 TCP Databases Do not expose to the internet

What port 9042 is used for

Cassandra and ScyllaDB native CQL client port.

Security: should port 9042 be open?

Do not expose to the internet. The default AllowAllAuthenticator means no login. Enable PasswordAuthenticator and client TLS and keep the port private.

IANA assignment

Port 9042 is in the registered range and has no IANA assignment. The usage above is unofficial but widespread.

Check what is listening on port 9042

Linux: is anything listening on TCP 9042?

sudo ss -tlnp 'sport = :9042'

Linux / macOS: which process owns the port

sudo lsof -nP -i :9042

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':9042 '

Windows (Command Prompt)

netstat -ano | findstr :9042

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 9042 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine

nc -vz -w 5 HOST 9042

From Windows

Test-NetConnection HOST -Port 9042

Block port 9042 in the firewall

ufw

sudo ufw deny 9042/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 9042 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 9042 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 9042' -Direction Inbound -Protocol TCP -LocalPort 9042 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.