This chapter describes the different types of topology groups and how to configure them. A topology
group is a named set of VLANs that share a Layer 2 control protocol. Topology groups simplify
configuration and enhance scalability of Layer 2 protocols by allowing you to run a single instance
of a Layer 2 protocol on multiple VLANs. One instance of the Layer 2 protocol controls all the VLANs.

For example, if a device is deployed in a Metro network and provides forwarding for two MRP rings
that each contain 128 VLANs, you can configure a topology group for each ring. If a link failure in a
ring causes a topology change, the change is applied to all the VLANs in the ring’s topology group.
Without topology groups, you would need to configure a separate ring for each VLAN.

You can use topology groups with the following Layer 2 protocols:

•

STP

•

MRP

•

VSRP

•

RSTP

Master VLAN and member VLANs

Each topology group contains a master VLAN and can contain one or more member VLANs and
VLAN groups:

•

Master VLAN – The master VLAN contains the configuration information for the Layer 2
protocol. For example, if you plan to use the topology group for MRP, the topology group’s
master VLAN contains the ring configuration information.