In a Layer 2 network, switches are often interconnected using redundant links to improve reliability. However, redundant links could bring loops at the same time, which may cause broadcast storm. To guarantee the network reliability and avoid loops at the same time, the best solution is STP (Spanning Tree Protocol).
Devices running STP can discover loops in the network and logically block some specific ports. Then a ring network can be disbranched to a loop-free tree structure network.
RSTP is similar with STP, but the speed of convergence is much faster than that of STP. For this reason, we recommend you choose RSTP instead of STP.
Typical Topologies
To make it simple to understand, here introduces three typical ring topologies. Both STP and RSTP can be applied to these topologies to avoid loops.
Although the topologies are different, the configurations of STP/RSTP are similar. This article will take the RSTP configuration of topology 1 as an example.
Note:
- Please configure STP/RSTP of switches first and then connect them together to avoid the broadcast storm.
- In this article, we only simply enable RSTP on the switches and the corresponding ports. The root switch, root ports, designated ports and blocked ports will be elected automatically. If you need to set a specific switch as the root port, or specify a port to be blocked, please set the CIST priority of the switch and the path cost of the ports according to your needs.
For the configuration of three switches are same, here we only take the configuration on switch 1 as an example.
Step 1:
Go to L2 FEATURES > Spanning Tree > STP Config page, enable Spanning Tree function globally and choose the mode as RSTP. Leave the other parameters as the default values.
Step 2:
Go to L2 FEATURES > Spanning Tree > Port Config page, enable Spanning Tree function for port 1/0/1 and 1/0/2. Leave the other parameters as the default values.
After the configurations on all switches are finished, connect them together as the topology shows. RSTP will decide which port should be blocked automatically. You can view the details on L2 FEATURES > Spanning Tree > STP Config > STP Summary page.
