How to verify node-to-node encryption for OpenDistro?

We have ES with Opendistro security plugin:

Node to Node encryption: https://opendistro.github.io/for-elasticsearch-docs/docs/security-configuration/ 1

How do we verify the node to node encryption is happening.

We sent an indexing request to Leader IP, and in the replica IP we saw tcpdump ( as internode communication is TCP ) but there was no luck.

Could someone help us how to verify node to node encryption?

Thanks,
Somebody