Final answer:
Routers are the devices that typically provide auto discovery services for smart devices on a network, using protocols like UPnP and Bonjour.
Step-by-step explanation:
The devices that provide auto discovery services for smart devices connected to a network are typically routers. Routers can support protocols such as Universal Plug and Play (UPnP) or Bonjour, which enable the automatic detection of network devices and services. While switches, hubs, and firewalls are significant components in a network, they do not usually handle the auto discovery process in a home or small office network environment. Switches facilitate communication between devices by forwarding data based on MAC addresses but don't manage device discovery or services between them. Hubs simply broadcast all network packets to every device on the network without intelligent routing, and firewalls are primarily security devices that control data flow based on security rules, not device discovery.