Port 9300 Elasticsearch transport · TCP

What runs on port 9300

Elasticsearch transport port: node-to-node communication inside the cluster (and the old Java transport client). Only cluster members should reach it; TLS on the transport layer is mandatory since 8.0.

Software that uses it: Elasticsearch · OpenSearch

Should port 9300 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.

• Discovery failures ("master not discovered") usually mean 9300 is blocked between nodes or discovery.seed_hosts is wrong.

Check port 9300

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :9300'
sudo lsof -i :9300

# from another machine: is it reachable?
nc -zv host 9300
nmap -p 9300 host
curl -v telnet://host:9300      # 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 9300

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 9300 proto tcp
sudo ufw deny 9300/tcp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 tcp dport 9300 accept
nft add rule inet filter input tcp dport 9300 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 9300 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 9300 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=9300 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 9300" with no source is just "open".

Related ports

• 9200 Elasticsearch
• 5601 Kibana

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