The link type provides a categorization for each port participating in RSTP by using the duplex mode on the port. Depending on what is attached to each port, two different link types can be identified:
- Point-to-Point - A port operating in full-duplex mode typically connects a switch to a switch and is a candidate for rapid transition to forwarding state.
- Shared - A port operating in half-duplex mode connects a switch to a hub that attaches multiple devices.
In the figure, click each link to learn about the link types.
The link type can determine whether the port can immediately transition to forwarding state, assuming certain conditions are met. These conditions are different for edge ports and non-edge ports. Non-edge ports are categorized into two link types, point-to-point and shared. The link type is automatically determined, but can be overridden with an explicit port configuration using the spanning-tree link-type parameter command.
Edge port connections and point-to-point connections are candidates for rapid transition to forwarding state. However, before the link-type parameter is considered, RSTP must determine the port role. Characteristics of port roles with regard to link types include the following:
- Root ports do not use the link-type parameter. Root ports are able to make a rapid transition to the forwarding state as soon as the port is in sync.
- Alternate and backup ports do not use the link-type parameter in most cases.
- Designated ports make the most use of the link-type parameter. Rapid transition to the forwarding state for the designated port occurs only if the link-type parameter is set to point-to-point.