VLAN Aggregation

VLAN aggregation is a feature aimed primarily at service providers.



This feature is supported only on the platforms listed for this feature in the license tables in the Feature License Requirements document.

The purpose of VLAN aggregation is to increase the efficiency of IP address space usage. It does this by allowing clients within the same IP subnet to use different broadcast domains while still using the same default router.

Using VLAN aggregation, a superVLAN is defined with the desired IP address. The subVLANs use the IP address of the superVLAN as the default router address. Groups of clients are then assigned to subVLANs that have no IP address, but are members of the superVLAN. In addition, clients can be informally allocated any valid IP addresses within the subnet. Optionally, you can prevent communication between subVLANs for isolation purposes. As a result, subVLANs can be quite small, but allow for growth without re-defining subnet boundaries.

Without using VLAN aggregation, each VLAN has a default router address, and you need to use large subnet masks. The result of this is more unused IP address space.

Multiple secondary IP addresses can be assigned to the superVLAN.

The following figure illustrates VLAN aggregation.

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VLAN Aggregation

In the preceding figure, all stations are configured to use the address for the default router.