What is the default network mode for a Docker container if none is specified?

In Docker, the default network mode for a container, if no specific mode is specified, is Bridge. The Bridge network mode creates a private internal network on your host machine, and containers can communicate with each other over this network. This mode isolates container traffic from the host machine's network and provides a layer of security and management.

When using the Bridge network, Docker automatically creates a virtual bridge, typically named docker0, that allows containers on the same bridge network to communicate with each other. Each container on the Bridge network can be assigned an IP address and can communicate using standard network protocols while maintaining the isolation from the host.

Bridge mode is particularly useful for lightweight applications or for when you need containers to communicate with each other but do not need them to expose their services directly on the host's network. This is often a common use case as it simplifies configuration and management of communication between services deployed in different containers.

The other options represent different networking behaviors that are not the default. Host mode gives containers direct access to the host network, while Overlay is used for multi-host networks, and None disables all networking for the container. Therefore, Bridge is the standard choice when creating containers without explicit networking instructions.