Difference between Root Port and Designated Port

Root Port: 

A Root Port is a single selected port that has the lowest Path Cost to the Root Bridge. The Root Port on the Bridge (Switch) is the port with the lowest Spanning Tree Path Cost from the switch to the Root Bridge.

• The root port is a direct link to the single root bridge or we can say it has the shortest path to the root bridge.
• If more than one connection connects to the root bridge, a port cost is calculated by evaluating the bandwidth of each link.

Advantages:

• Efficient: The root port is responsible for forwarding traffic to the root bridge, which helps ensure efficient network operation.
• High speed: The root port typically has the highest bandwidth capacity, making it suitable for transferring large amounts of data.
• Simple: The root port is easy to configure and requires minimal maintenance.

Disadvantages:

• Limited scalability: Root ports can become a bottleneck if the network grows too large, as they are responsible for forwarding all traffic to the root bridge.
• Vulnerability: The root port is vulnerable to network outages and other disruptions, as it is a single point of failure in the network.
• Limited redundancy: The root port has limited redundancy, as it cannot be used as a backup if another port fails.

Designated Port:

The designated port has the lowest spanning-tree path cost on a specific Local Area Network(LAN). The path cost depends on the speed of the bridge port interface. The cost of each port on either side of the segment and the total cost computed by STP for that port to go back to the root bridge are used to choose designated ports on a per-segment basis.

• A bridge may have numerous Designated Ports (Switch).
• A Root Bridge’s (Root Switch’s) ports are all Designated Ports, and there is no Root Port on a Root Bridge (Root Switch).

Advantages:

• Redundancy: Designated ports provide redundancy in the network, allowing traffic to be rerouted if a port fails.
• Efficient: Designated ports help ensure efficient network operation by forwarding traffic only where it is needed.
• Scalable: Designated ports can be added to the network as it grows, helping ensure that the network remains functional and efficient.

Disadvantages:

• Complexity: Designated ports can be more complex to configure and maintain than root ports, as they require more advanced network knowledge.
• Slower speed: Designated ports typically have lower bandwidth capacity than root ports, making them less suitable for transferring large amounts of data.
• Increased network traffic: Designated ports can increase network traffic by forwarding unnecessary traffic to other ports, which can lead to network congestion.

Let’s see the difference between Root Port and Designated Port:

Root Port	Designated Port
A single selected port on a switch, other than root switch.	The designated port is the port on every switch(root/non-root switch).
Least path cost from a non-root bridge to reach the root bridge.	Lowest STP cost on a particular local area network (LAN) segment to the root bridge.
Only one root port is presents on a non-root switch.	There may be multiple designated ports presents on a switch(root/non-root).
No root ports are present on a root switch.	All ports of root switch are designated ports.
One end If root port, opposite will be designated port (never be blocking port).	One end is the designated port, opposite will be either the designated port or non-designated port.
Used for forwarding traffic towards the root bridge.	Used for forwarding traffic away from the root bridge.
The port that is closest to the root bridge.	The port that is responsible for forwarding traffic on a particular segment or network.

Conclusion :

Root ports and designated ports are two types of ports used in the STP algorithm. Root ports are located on non-root switches and forward data traffic towards the root bridge, while designated ports are located on network segments and forward data traffic towards the root bridge from a specific network segment. The selection and state of these ports are determined based on their path cost to the root bridge. Understanding the differences between these two types of ports is essential for network engineers to design and maintain efficient and reliable network topologies.