Why is stp used

Special Offer. Valid first name is required. Valid last name is required. Please enter a valid email address for shipping updates. Skip to content Skip to search Skip to footer. Available Languages. Download Options. Updated: December 11, Contents Introduction. Prerequisites Requirements There are no specific requirements for this document.

For the examples, this document used: A console cable that is suitable for the Supervisor Engine in the switch Six Catalyst Switches The information in this document was created from the devices in a specific lab environment. However, when STP runs on both switches, the network logically looks like this: This information applies to the scenario in the Network Diagram : Switch 15 is the backbone switch.

Switches 12, 13, 14, 16, and 17 are switches that attach to workstations and PCs. Description of the Technology With STP, the key is for all the switches in the network to elect a root bridge that becomes the focal point in the network.

Clients end stations on Switch Ports You can also issue the set spantree portfast command, on a per-port basis. Leave most other STP variables at their default values. After the root switch identification, the switches adhere to these rules: STP Rule 1 —All ports of the root switch must be in forwarding mode. STP Rule 2 —The root port must be set to forwarding mode. Step-by-Step Instructions Complete these steps: Issue the show version command in order to display the software version that the switch runs.

Note: All switches run the same software version. VLAN 1 bridge max aging time set to VLAN 1 bridge hello time set to 2. VLAN 1 bridge forward delay set to Switch is now the root switch for active VLAN 1. VLAN bridge max aging time set to VLAN bridge hello time set to 2. VLAN bridge forward delay set to Switch is now the root switch for active VLAN VLANs 1, bridge max aging time set to VLANs 1, bridge hello time set to 2.

VLANs 1, bridge forward delay set to Switch is now the root switch for active VLANs 1, Connecting hubs, concentrators, switches, bridges, etc. Use with caution. Verify This section provides information you can use to confirm that your configuration works properly.

If an active link fails, STP activates a running standby link with the highest priority to ensure network connectivity. Three elements are involved in trimming a ring network into a tree network: root bridge, root port, and designated port.

A PID is composed of a port priority and a port number. After the root bridge, root port, and designated ports are selected successfully, a tree topology is set up on the entire network. When the topology is stable, only the root port and designated ports forward traffic. Figure 2 shows the format of an Ethernet frame. Each bridge actively sends configuration BPDUs during initialization.

After the network topology becomes stable, only the root bridge proactively sends configuration BPDUs. If both fields are the same as those on the receive port, the bridge discards the configuration BPDU. Therefore, the bridge does not need to process BPDUs with the same information as the local port. During network initialization, every device considers itself the root bridge and sets the root ID to its own BID. All the ports on the root bridge are in Forwarding state. The port with the lowest sender BID.

The lowest port number of the sending switch. Rapid spanning tree protocol RSTP is as its name suggests, a faster transition to a port-forwarding state.

An alternate port receives BPDUs from another switch but remains in a blocked state. It will elect one of the two ports as a root port and the other will become an alternate port.

If at any time the root port fails, this redundant path—the alternate port—will become the new root port. A backup port receives BPDUs from its own switch but remains in a blocked state. For example, If a switch has two ports connecting to different switches, then one port will be elected as a root port and the other will become the backup port.