Encrypted traffic between containers on single-host swarm cluster


I have been trying to check whether the traffic between containers in a single-node host is encrypted but I haven’t managed yet to capture the traffic, not even the cleartext one, so probably I’m doing something wrong.
Anyway I wanted to ask if you know and if you have verified that when creating an overlay network for the swarm using the --opt encrypted, this is valid also for traffic between containers deployed on the same host.