Port 9300 (TCP) — Elasticsearch transport

Check if port 9300 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':9300 '

From another machine, test reachability:

nc -zv your-server.example.com 9300

Block port 9300 from the internet

With UFW (Ubuntu/Debian):

sudo ufw deny 9300

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=9300/tcp && sudo firewall-cmd --reload

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