9042 Cassandra-CQL TCP
Reference for TCP port 9042, commonly associated with Cassandra-CQL.
What it's for
Port 9042 is the default client port for Apache Cassandra, the distributed wide-column NoSQL database built for high write throughput and horizontal scalability across many nodes with no single point of failure. Applications connect on this port using CQL (Cassandra Query Language, a SQL-like syntax) to read and write data.
Protocol basics
Client connections use the CQL native protocol over TCP, a binary protocol specifically designed for Cassandra's data model and distributed architecture. This is distinct from the ports Cassandra nodes use to communicate with each other internally (7000/7001) — 9042 is specifically the client-facing entry point applications and drivers connect to. Cassandra's architecture means any node can typically handle a client request and coordinate with other nodes as needed, so drivers are usually configured with multiple contact points rather than a single hardcoded host.