BigIron RX Series Configuration Guide 43953-1001986-01Chapter16Topology GroupsTopology overviewThis chapter describes the different types of topology groups and how to configure them. A topologygroup is a named set of VLANs that share a Layer 2 control protocol. Topology groups simplifyconfiguration and enhance scalability of Layer 2 protocols by allowing you to run a single instanceof 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 ringsthat each contain 128 VLANs, you can configure a topology group for each ring. If a link failure in aring 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• RSTPMaster VLAN and member VLANsEach topology group contains a master VLAN and can contain one or more member VLANs andVLAN groups:• Master VLAN – The master VLAN contains the configuration information for the Layer 2protocol. For example, if you plan to use the topology group for MRP, the topology group’smaster VLAN contains the ring configuration information.• Member VLANs – The member VLANs are additional VLANs that share ports with the masterVLAN. The Layer 2 protocol settings for the ports in the master VLAN apply to the same ports inthe member VLANs. A change to the master VLAN’s Layer 2 protocol configuration or Layer 2topology affects all the member VLANs. Member VLANs do not independently run a Layer 2protocol.• Member VLAN groups – A VLAN group is a named set of VLANs. The VLANs within a VLANgroup have the same ports and use the same values for other VLAN parameters.When a Layer 2 topology change occurs on a port in the master VLAN, the same change is appliedto that port in all the member VLANs that contain the port. For example, if you configure a topologygroup whose master VLAN contains ports 1/1 and 1/2, a Layer 2 state change on port 1/1 appliesto port 1/1 in all the member VLANs that contain that port. However, the state change does notaffect port 1/1 in VLANs that are not members of the topology group.
