The Spanning Tree Protocol (STP) is a network protocol that ensures the loop-free topology of any Ethernet-based LAN. STP allows network administrators to configure a redundant network infrastructure without letting the data flow uncontrollably as a result of an infinite loop. The STP makes this possible by creating a tree-like topology throughout the network, which ensures that there are no redundant links between network devices.
While it is essential for STP to coexist with the physical topology of the network, network administrators must comprehend how STP operates to make changes and upgrades to the network infrastructure. One of the fundamental concepts of STP is the priority level. Understanding STP priority is crucial because it helps network administrators designate the root bridge and the designated port for each segment of the network.
This article will provide a comprehensive guide to STP priority and how it works.
What is STP Priority?
Every device connected to the LAN network uses the STP protocol to detect redundant links. The most crucial element of this protocol is the designation of a single bridge as the root bridge. This bridge becomes the center of the network, and all other device bridges use it as a reference point to calculate the cost of transmitting data.
The root bridge in an STP network is assigned a priority value, which ranges from 0 to 65535. The bridge with the lowest priority value is elected as the root bridge. The default priority value is 32768. This priority value is configurable, which allows network administrators to manipulate the selection process of the root bridge.
The Process of Electing a Root Bridge
During the initialization process of an STP network, every device sends out Bridge Protocol Data Units (BPDU) to other switches in the network. The BPDU contains information about the device, including the priority value, MAC address, and port ID. Every switch in the network receives and interprets the BPDU before forwarding it to other connected devices.
All switches examine the content of the BPDU and compare their priority value with that of the sending switch. If any switch detects a sending switch with a lower priority value than its own, it replaces its priority value with that of the incoming BPDU and forwards the BPDU to other connected devices. This process continues until the BPDU reaches the switch with the lowest priority value.
When the root bridge is elected, every other switch in the network sets its best path to the root bridge and starts forwarding data to other switches. This process carries a designated port for each segment of the network. A designated port is a port in a switch that directly connects the switch to the root bridge.
Configuring STP Priority
The default STP priority setting is appropriate for most network configurations. However, it is possible to change the priority value of a bridge to select it as the root bridge. The following is the procedure for configuring STP priority on a switch;
1. To configure STP priority, you need to access the switch configuration environment. When you access the configuration environment, navigate to the interface for the required Ethernet port to be modified.
2. Enter the access interface configuration command for the interface. The command depends on the model of switch in use.
3. Enter the spanning-tree bridge priority command to change the priority of the bridge. The priority value ranges between 0 and 65535. A lower priority value represents a higher priority.
4. Finally, exit the configuration environment.
Conclusion
In conclusion, STP priority is an essential aspect of STP network configuration that enables the proper selection of the root bridge. By setting a priority value for a bridge, network administrators can manipulate the selection process and effectively manage their network topology. Understanding the STP priority concept is crucial for network administrators to troubleshoot and maintain a stable and secure network infrastructure.