9300
Elasticsearch inter-node cluster communication
Elasticsearch Cluster Communication
What is port 9300?
Port 9300 is used for the Elasticsearch binary transport protocol, handling inter-node communication within a cluster including data replication, shard allocation, and cluster state synchronization. It must be accessible only between cluster nodes on a private network. An exposed port 9300 could allow an attacker to inject a malicious node into the cluster.
Quick checks
$
nc -zv example.com 9300
$
nmap -p 9300 example.com
$
telnet example.com 9300