Understanding Layer 2 Virtual Switches

On MX Series routers only, you can group one or more bridge domains to form a virtual switch to isolate a LAN segment with its spanning-tree protocol instance and separate its VLAN ID space. A bridge domain consists of a set of logical ports that share the same flooding or broadcast characteristics. Like a virtual LAN, a bridge domain spans one or more ports of multiple devices. You can configure multiple virtual switches, each of which operates independently of the other virtual switches on the routing platform. Thus, each virtual switch can participate in a different Layer 2 network.

You can configure a virtual switch to participate only in Layer 2 bridging and optionally to perform Layer 3 routing. In addition, you can configure one of three Layer 2 control protocols—Spanning-Tree Protocol, Rapid Spanning-Tree Protocol (RSTP), or Multiple Spanning-Tree Protocol (MSTP)—to prevent forwarding loops. For more information about how to configure Layer 2 logical ports on an interface, see the Junos OS Network Interfaces Library for Routing Devices.

In Junos OS Release 9.2 and later, you can associate one or more logical interfaces configured as trunk interfaces with a virtual switch. A trunk interface, or Layer 2 trunk port, enables you to configure a logical interface to represent multiple VLANs on the physical interface. Packets received on a trunk interface are forwarded within a bridge domain that has same VLAN identifier. For more information about how to configure trunk interfaces, see the Junos OS Network Interfaces Library for Routing Devices.

You can also configure Layer 2 forwarding and learning properties for the virtual switch as well as any bridge domains that belong to a virtual switch. .

For more information about configuring a routing instance for Layer 2 VPN, see the Junos OS VPNs Library for Routing Devices. .