Layer 2 VLANs Overview

You can configure one or more VLANs to perform Layer 2 bridging. The Layer 2 bridging functions include integrated routing and bridging (IRB) for support for Layer 2 bridging and Layer 3 IP routing on the same interface, and virtual switches that isolate a LAN segment with its spanning-tree protocol instance and separate its VLAN ID space.

A VLAN is a set of logical ports that share the same flooding or broadcast characteristics and span one or more ports of multiple devices.

You can configure one or more VLANs to perform Layer 2 bridging. Thus, MX Series routers or EX Series switches can function as Layer 2 switches, each with multiple bridging, or broadcast, domains that participate in the same Layer 2 network. You can also configure Layer 3 routing support for a VLAN. Integrated routing and bridging (IRB) provides support for Layer 2 bridging and Layer 3 IP routing on the same interface. IRB enables you to route packets to another routed interface or to another VLAN that has a Layer 3 protocol configured.

You can also group one or more VLANs within a single instance, or virtual switch. Multiple virtual switches, each of which operates independently of other virtual switches on the device, are supported. Virtual switches isolate a LAN segment with its spanning-tree protocol instance and separate its VLAN ID space. Thus, each virtual switch can participate in a different Layer 2 network.

VLANs provide support for a Layer 2 trunk port. A Layer 2 trunk interface enables you to configure a single logical interface to represent multiple VLANs on a physical interface. You can configure a set of VLANs and VLAN identifiers that are automatically associated with one or more Layer 2 trunk interfaces. Packets received on a trunk interface are forwarded within a VLAN that has the same VLAN identifier. A Layer 2 trunk interface also supports IRB within a VLAN. In addition, you can configure Layer 2 learning and forwarding properties that apply to the entire set of VLANs.

You can configure VPLS ports in a virtual switch instead of a dedicated routing instance of type vpls so that the logical interfaces of the Layer 2 VLANs in the virtual switch can handle VPLS routing instance traffic. Packets received on a Layer 2 trunk interface are forwarded within a VLAN that has the same VLAN identifier.