STP per VLAN group

STP per VLAN group is an STP enhancement that provides scalability while overcoming the limitations of the following scalability alternatives:

  • Standard STP - You can configure up to 254 instances of standard STP on a RUCKUS device. However, on RUCKUS ICX 7150 device only 253 STP instances are supported. More instances of STP may be required in large configurations. Using STP per VLAN group, you can aggregate STP instances.
  • Single STP - Single STP allows all the VLANs to run STP, but each VLAN runs the same instance of STP, resulting in numerous blocked ports that do not pass any Layer 2 traffic. STP per VLAN group uses all available links by load balancing traffic for different instances of STP on different ports. A port that blocks traffic for one spanning tree forwards traffic for another spanning tree.

STP per VLAN group allows you to group VLANs and apply the same STP parameter settings to all the VLANs in the group. The following figure shows an example of a STP per VLAN group implementation.

Figure 1. STP per VLAN group example

A master VLAN contains one or more member VLANs. Each of the member VLANs in the STP Group runs the same instance of STP and uses the STP parameters configured for the master VLAN. In this example, the FastIron switch is configured with VLANs 3, 4, 13, and 14. VLANs 3 and 4 are grouped in master VLAN 2, which is in STP group 1. VLANs 13 and 14 are grouped in master VLAN 12, which is in STP group 2. The VLANs in STP group 1 all share the same spanning tree. The VLANs in STP group 2 share a different spanning tree.

All the ports are tagged. The ports must be tagged so that they can be in both a member VLAN and the member's master VLAN. For example, ports 1/1/1 - 1/1/4 are in member VLAN 3 and also in master VLAN 2 (since master VLAN 2 contains member VLAN 3).