Which type of port on a switch tags frames with a VLAN number?

A trunk port is designed to carry traffic for multiple VLANs across the same physical link between network devices. When a switch uses trunk ports, it tags frames with a VLAN number using protocols like 802.1Q. This tagging allows the receiving device to determine the VLAN to which the frame belongs, thus enabling proper routing and switching of traffic between different VLANs.

In contrast, access ports are typically meant for end devices and are assigned to a single VLAN without any tagging. Control and service ports are not standard terms used in relation to VLAN tagging in networking, thus affirming that trunk ports are the correct answer in this context.