7001 Cassandra-internode-ssl TCP

What it's for

Port 7001 is the encrypted counterpart to port 7000 for Cassandra internode communication — used when SSL/TLS encryption is enabled for traffic between cluster nodes. It carries the same gossip and data-replication traffic as port 7000, just with the added encryption layer for deployments where inter-node traffic crosses networks that aren't fully trusted.

Protocol basics

The underlying internode protocol is identical to port 7000's; the distinction is purely that connections on 7001 are wrapped in TLS. Enabling internode encryption is a configuration choice (server_encryption_options in Cassandra's config) rather than a protocol requirement, since many Cassandra clusters run entirely within a single trusted private network or VPC where the operational overhead of internode TLS may be judged unnecessary — though it's the safer default for any cluster spanning multiple data centers or less tightly controlled network segments.