Cassandra - Setup replication on 2 physcial machines

I want to setup Replication on two systems. So, need suggestions for the same . I have following doubts :-

1) Is it possible to setup replication on two physical machines ?
2) If Yes, What should be the keyspace Schema ?
3) CREATE KEYSPACE ums_db WITH replication = {'class': 'NetworkTopologyStrategy', 'DC1': '3', 'DC2': '3'} ;

What does above schema means that I need to have 6 physical machines or just 2 physical machines where 3 nodes are logically created to store copies of data on each physical datacenter ?

4) What is the best schema for creating replication with 2 physical machines and what all files need to be changed and how ?

Thanks,