When a Docker Swarm is created or a docker host joins the swarm two networks are created.

• an overlay network called ingress, which manages control and data traffic related to swarm services. This is the default network unless the USER specifies other user-defined overlay networks. User-defined overlay networks COULD be created by using the command “docker network create”ingress network facilitates load BALANCING among a service’s nodes.
• To encrypt the application data traffic on a given overlay network, use the --opt encrypted flag on docker network create.
• To attach a service to an existing overlay network, use the --network flag to docker service create, or the --network-add flag to docker service update command. Service containers connected to an overlay network can communicate with each other through it.
• a bridge network called docker_gwbridge, which connects the Docker daemon to the other docker daemons in a swarm. docker_gwbridge connects the overlay networks (including the ingress network) to an individual Docker daemon’s physical network. It is a VIRTUAL bridge that exists in the kernel of the docker host. For customising the bridge network we have to do that before docker host joins the swarm or by temporarily removing the host from the swarm.