440 BigIron RX Series Configuration Guide53-1001986-01Master VLANs and customer VLANs in MRP16Master VLANs and customer VLANs in MRPA topology group enables you to control forwarding in multiple VLANs using a single instance of aLayer 2 protocol such as MRP. For more information on topology group and MRP, refer to “MasterVLANs and customer VLANs in a topology group” on page 400.Control ports and free portsA port in a topology group can be a control port or a free port:• Control port – is a port in the master VLAN and therefore controlled by the Layer 2 protocolconfigured in the master VLAN. The same port in all the member VLANs is controlled by themaster VLAN’s Layer 2 protocol. Each member VLAN must contain all of the control ports (allother ports in the member VLAN are “free ports.”).• Free port – is not controlled by the master VLAN’s Layer 2 protocol. The master VLAN cancontain free ports. (In this case, the Layer 2 protocol is disabled on those ports.) In addition,any ports in the member VLANs that are not also in the master VLAN are free ports.NOTESince free ports are not controlled by the master port’s Layer 2 protocol, they are assumed toalways be in the Forwarding state when enabled.Configuration considerations• You can configure up to 256 topology groups. Each group can control up to 4094 VLANs. AVLAN cannot be controlled by more than one topology group.• The topology group must contain a master VLAN and can also contain individual memberVLANs, VLAN groups, or a combination of individual member VLANs and VLAN groups.Therefore, configure the master VLAN and member VLANs or member VLAN groups before youconfigure a topology group.• Once you add a VLAN as a member of a topology group, all the Layer 2 protocol information onthe VLAN is deleted.• If you add a new master VLAN to a topology group that already has a master VLAN, the newmaster VLAN replaces the older master VLAN. All member VLANs and VLAN groups follow theLayer 2 protocol settings of the new master VLAN.• If you remove the master VLAN (by entering no master-vlan ), the software selects thenew master VLAN from member VLANs. A new candidate master-vlan will be in configuredorder to a member VLAN so that the first added membe VLAN will be a new candidate masterVLAN. Once you saved and reloaded, a member VLAN with the newest VLAN ID will be thenewcandidate master. The new master VLAN inherits the Layer 2 protocol settings of the oldermaster VLAN.• Once you add a VLAN or VLAN group as a member of a topology group, all the Layer 2 protocolconfiguration information for the VLAN or group is deleted. For example, if STP is configured ona VLAN and you add the VLAN to a topology group, the STP configuration is removed from theVLAN. Once you add the VLAN to a topology group, the VLAN uses the Layer 2 protocol settingsof the master VLAN.
