Which device will always have all of its ports in the same collision domain?
Open Systems Interconnect (OSI) Layer 1 devices, such as hubs and repeaters, do not create multiple collision domains. All of their ports remain in the same collision domain as well as the same broadcast domain.
A collision domain is a domain where two or more devices in the domain could cause a collision by sending frames at the same time. Each switch port is a separate collision domain. Replacing a hub with a switch effectively eliminates collisions for devices connected to the switch ports.
Bridges and switches create multiple collision domains and can reduce collisions within a broadcast domain, as each port constitutes a separate collision domain. However, if the network is not segmented with Virtual LANs (VLANs), all ports remain in the same broadcast domain. The main difference between a bridge and a switch is that the latter has a higher port capacity and better performance. VLANs segment the network into smaller broadcast domains using a Layer 2 device such as switch.
Routers segment the network into multiple broadcast domains. Routers are Layer 3 devices, and thus they interconnect different Layer 3 IP networks. Every interface/subinterface on a router has a unique IP network/subnet address that corresponds to a broadcast domain. Thus, every interface on a router defines a broadcast domain.