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CLI-based Configuration Guide - Ethernet Switching

AR650, AR1600, and AR6100 V300R003

This document describes how to configure the components for LAN services, including link aggregation groups, VLANs, voice VLANs, MAC address tables, transparent bridging, as well as GVRP, STP/RSTP, and MSTP protocols.
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Overview of VLAN Aggregation

Overview of VLAN Aggregation


VLAN aggregation, also called super-VLAN, partitions a broadcast domain into multiple VLANs (sub-VLANs) on a physical network and aggregates the sub-VLANs into a single logical VLAN (super-VLAN). The sub-VLANs use the same IP subnet and default gateway address.


VLAN technology is widely applied to packet switching networks because it is capable of flexibly controlling broadcast domains and is easy to deploy. Usually, a router uses a Layer 3 logical interface in each VLAN to allow hosts in different broadcast domains to communicate. This wastes IP addresses. On a subnet corresponding to a VLAN, the subnet ID, directed broadcast address, and subnet default gateway address cannot be used as IP addresses of hosts in the VLAN. In addition, the number of hosts on a subnet may be less than the number of IP addresses available in the subnet. These remaining IP addresses are essentially wasted because they cannot be used by other VLANs.

As shown in Figure 4-1, VLAN 2 requires 10 host addresses. The subnet with a 28-bit mask is assigned to VLAN 2, where is the subnet ID, is the directed broadcast address, and is the default gateway address. Hosts cannot use these three addresses, but the other 13 addresses ranging from to are available to them.

VLAN 2 requires only 10 IP addresses, the remaining 3 IP addresses cannot be used by other VLANs and are wasted. If more VLANs are added, more IP addresses will be wasted.

Figure 4-1  Networking of a common VLAN

VLAN aggregation is used to solve the preceding problem. VLAN aggregation maps each sub-VLAN to a broadcast domain, associates a super-VLAN with multiple sub-VLANs, and assigns only one IP subnet to the super-VLAN. This ensures that all sub-VLANs share the IP address of the associated super-VLAN as the gateway IP address, effectively implementing Layer 3 connectivity.

Sub-VLANs share one gateway address so that the number of subnet IDs, subnet default gateway addresses, and directed broadcast IP addresses used is reduced. The switch assigns IP addresses to hosts in sub-VLANs according to the actual number of hosts, ensuring that each sub-VLAN is used as an independent broadcast domain to implement isolation. Therefore, VLAN aggregation conserves IP addresses and implements flexible addressing.

Updated: 2019-04-12

Document ID: EDOC1100041791

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