Technical Documentation
Layer 2 Features for a Switching Environment
Juniper Networks MX Series 3D Universal Edge Routers include all standard Ethernet capabilities as well as enhanced mechanisms for service providers to provision and support large numbers of Ethernet services in addition to all Layer 3 services. The MX Series routers include several features to contain and control the Ethernet environment.
One of these features is the virtual switch. MX Series routers allow the collapsing of multiple diverse switch networks to a single platform by running virtual instances of as many Spanning Tree Protocols (STPs) as needed to support all broadcast domains. This is important because there are many incompatible versions of STP, and without a way to run multiple virtual instances, a separate switch would be needed to support each one. With MX Series virtual switch configuration, you can continue to running existing STP protocols with the option to migrate to a common STP protocol if desired.
Virtual switches also make it easy to separate independent switched Ethernet networks, each possibly carrying several VLANs. Because the same VLAN ID can be used in multiple switched networks, virtual switches can keep each VLAN and broadcast domain logically separated.
 | Note: In a router environment, there is always a default routing instance. When you need only one routing instance on the router, you use the default routing instance without qualification. However, if you need more than one routing instance, you must configure statements to create additional routing instances. In a switching environment, the same is true of virtual switches: if you need more than one virtual switch in addition to the “default,” you must create them. |
For more information about STPs and virtual switches, see the Junos OS Layer 2 Configuration Guide 
.
