> # About VLANs for Gigabit Ethernet

> Virtual LANs (VLANs) create multiple virtual Layer 2 networks over a physical LAN network. VLANs provide traffic isolation, security, and broadcast control.

> Gigabit Ethernet ports automatically recognize Ethernet frames with IEEE 802.1Q VLAN encapsulation. If you need to have traffic from multiple VLANs terminated on one Gigabit Ethernet port, configure subinterfaces—one for each VLAN.

> Note If the IPS module or MPS-14/2 module is connected to a Cisco Ethernet switch, and you need to have traffic from multiple VLANs coming to one IPS port, verify the following requirements on the Ethernet switch:

> - The Ethernet switch port connected to the IPS module or MPS-14/2 module is configured as a trunking port.
> - The encapsulation is set to 802.1Q and not ISL, which is the default.

> Use the VLAN ID as a subscription to the Gigabit Ethernet interface name to create the subinterface name:

> `slot-number / port-number.VLAN-ID`

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