My network settings: 

DC2 : Node-3

root@mongoDBpoc1:~/DSE/node1/resources/cassandra/bin# cat ~/DSE/node1/resources/cassandra/conf/cassandra.yaml | grep 10.0.4.5
listen_address: 10.0.4.5
rpc_address: 10.0.4.5
native_transport_address: 10.0.4.5
root@mongoDBpoc1:~/DSE/node1/resources/cassandra/bin# cat ~/DSE/node1/resources/cassandra/conf/cassandra.yaml | grep 52.156.71.71
broadcast_address: 52.156.71.71
broadcast_rpc_address: 52.156.71.71

- seeds: "104.40.19.81"


DC1 : Node-1

root@MongoDBpoc:~/DSE/node/resources/cassandra/tools/bin# cat ~/DSE/node/resources/cassandra/conf/cassandra.yaml | grep 10.0.5.4
listen_address: 10.0.5.4
rpc_address: 10.0.5.4
native_transport_address: 10.0.5.4
root@MongoDBpoc:~/DSE/node/resources/cassandra/tools/bin# cat ~/DSE/node/resources/cassandra/conf/cassandra.yaml | grep 104.40.19.81
          - seeds: "104.40.19.81"
broadcast_address: 104.40.19.81
broadcast_rpc_address: 104.40.19.81

DC1 : Node2 

root@mongodbPoc2:~/DSE/node2/bin# cat ~/DSE/node2/resources/cassandra/conf/cassandra.yaml | grep 10.0.5.5
listen_address: 10.0.5.5
rpc_address: 10.0.5.5
native_transport_address: 10.0.5.5
root@mongodbPoc2:~/DSE/node2/bin# cat ~/DSE/node2/resources/cassandra/conf/cassandra.yaml | grep 23.99.66.193
broadcast_address: 23.99.66.193
broadcast_rpc_address: 23.99.66.193
root@mongodbPoc2:~/DSE/node2/bin#

 - seeds: "104.40.19.81"