Objective

Loops in a network occur when alternate routes exist between hosts. Loops in an extended network can cause Layer 2 switches to forward traffic indefinitely, which results in increased traffic and reduced network efficiency. Spanning Tree Protocol (STP) provides a single path between any two end stations in order to prevent loops. Rapid Spanning Tree Protocol (RSTP) detects network topologies to provide faster convergence and create a network without loops. This is most effective when the network topology is naturally tree structured.

This article explains how to configure RSTP per port on the 300 Series Managed Switches.

Applicable Devices

• SG300-10PP

• SG300-10MPP

• SG300-28PP-R

• SG300-28SFP-R

• SF302-08MPP

• SF302-08PP

• SF300-24PP-R

• SF300-48PP-R

Software Version

• 1.4.0.00p3 [SG300-28SFP-R]

• 6.2.10.18 [All other Applicable Devices]

Spanning Tree Global Setup

First, you need to make sure the parameters for RSTP are enabled in the switch.

Step 1. Log in to the web configuration utility and choose Spanning Tree > STP Status & Global Settings. The STP Status & Global Settings page opens:

Step 2. Check the Enable check box in the Spanning Tree field to enable STP.

Step 3. Click the Rapid STP radio button in the STP Operation Mode field to use RSTP as the operation mode of STP.

Step 4. Click on of the available options in the BPDU Handling field to handle Bridge Protocol Data Unit (BPDU) packets when STP is disabled:

• Filtering — This is based on source MAC address. With this option the switch determines that the destination of the MAC is on the same network or subnet so it does not forward the packet and drops it. This option determines whether to drop or send the packet for desired destination.

• Flooding — The packet is flooded out of all forwarding ports in its VLAN (except the port it was received on). Extra attack of packets overruns the table and causes a fail-over situation because switch has a limited amount of memory to store MAC addresses. Data is bridged exclusively to the network segment containing the computer that the data is specifically destined for.

Step 5. Click on one of the available options in the Path Cost Default Values field to assign default path costs:

• Short — This option uses a range from 1 to 65,535 for port path costs.

• Long — This option uses a range from 1 to 200,000,000 for port path costs.

Step 6. Click Apply to save your settings.

Enable Rapid Spanning Tree on a Port

Step 1. Log in to the web configuration utility and choose Spanning Tree > RSTP Interface Settings. The RSTP Interface Settings page opens:

Step 2. If a connected device is discovered via STP, choose the interface that is connected to the device and click Activate Protocol Migration. This performs a test on the connected device to see the type of STP. The switch then communicates with the connected device through the use of the respective STP type of the connected device

Step 3. In the Filter drop-down list, choose whether to configure a port or a LAG (Link Aggregation Group).

Step 4. Click the radio button of the port /LAG you want to enable RSTP.

Step 5. Click Edit. The Edit RSTP Interface Settings window appears.

Step 6. In the Point to Point Administrative Status field, click one of the available options:

Note: Ports defined as Full Duplex are considered Point-to-Point port links.

• Enable — Enable feature helps to make this port as a RSTP edge port and brings it to forwarding mode quicker than normal STP.

• Disable — Disable feature helps the port not be considered as point-to-point for RSTP purposes, STP will work on regular speed.

• Auto — Determines switch status it self with the help of RSTP BPDUs.

The following information about the port/LAG is displayed:

• Point to Point Operational Status — Displays enabled if point-to-point administrative distance is set to auto.

• Role — The role of the port as assigned by STP to provide STP path.

• Mode — The current spanning tree mode.

• Fast Link Operational Status — The status of the fast link.

• Port Status — RSTP status on the port.

Step 7. Click Apply to save your changes.