Spanning-tree standards
The STP is an open source Layer 2 loop prevention mechanism that is enabled on switches by default. STP is defined by IEEE 802.1D. However, Cisco does not implement the IEEE 802.1D version of spanning-tree on their devices.
Port roles and states
In this section, you will learn about the various port roles and states involved when an interface transitions into forwarding or blocking traffic.
The following are the port roles used in spanning-tree:
- Root ports: These are the ports that are closest to the root bridge. If you recall, each switch always points toward the root bridge at the end of the election process. This means that each switch has a root port that points back to the root bridge on the network. Root ports are never on the root bridge itself.
- Designated ports: These are what are known as non-root ports, which are still always able to forward traffic between devices on the network.
- Alternate or backup ports: These are interfaces...
