Bridge acts as a virtual private network in docker. Each container in the same private network can communicate with each other without any port but if it has to communicate with the host machine then port is required to open the connection with host.
Docker Image
Tagging image in docker
Tag to an image can be added during build or explicit using docker tag
docker tag SOURCE_IMAGE[:TAG] TARGET_IMAGE[:TAG]
Example
docker tag ubuntu ubuntutest (This will create an copy of the ubuntu image with ubuntutest name, we can also specify a particular custom tag)