I was exposing port 7000 of cassandra to 0.0.0.0:9042 . I needed to map port 9042 of cassandra to 0.0.0.0:9042 . As cassandra's CQL client connections listens to port 9042.
As in docker
docker stop cassandradb
docker rm cassandradb
docker run -d --name cassandradb -p 9042:9042 cassandra
It fixes the Cassandra connection.