Configuring a Layer 2 Virtual Switch with a Layer 2 Trunk Port

You can associate one or more Layer 2 trunk interfaces with a virtual switch. A Layer 2 trunk interface enables you to configure a logical interface to represent multiple VLANs on the physical interface. Within the virtual switch, you configure a bridge domain and VLAN identifier for each VLAN identifier configured on the trunk interfaces. Packets received on a trunk interface are forwarded within a bridge domain that has the same VLAN identifier. Each virtual switch you configure operates independently and can participate in a different Layer 2 network.

A virtual switch configured with a Layer 2 trunk port also supports IRB within a bridge domain. IRB provides simultaneous support for Layer 2 bridging and Layer 3 IP routing on the same interface. Only an interface configured with the interface-mode (access | trunk) statement can be associated with a virtual switch. An access interface enables you to accept packets with no VLAN identifier. For more information about configuring trunk and access interfaces, see the Junos OS Network Interfaces Library for Routing Devices.

In addition, you can configure Layer 2 learning and forwarding properties for the virtual switch.

To configure a virtual switch with a Layer 2 trunk interface, include the following statements:

Layer 2 trunk ports are used in two distinct types of virtual switch configuration. One method is called service provider style and the other is called enterprise style. The two methods can be confusing because both methods involve configuring interfaces known as trunk interfaces. However, both types of configuration are distinct.

Service provider style and enterprise style each have benefits and drawbacks.

• Service provider style—Offers more control, but requires more care in configuration. Service providers can use all bridging features in any shape or size, but for large bridged designs, customization requirements quickly grow.

• Enterprise style—Offers a single Layer 2 network connected by simple bridges. Easier to use, but more limited in function. Configuration is simple and straightforward and condensed.

The easiest way to understand the differences in configuration of the two styles is to compare them using the same interfaces and VLAN IDs.

You can configure multiple bridge domains between the same pair of Ethernet interfaces, for example, xe-0/0/1 and xe-0/0/2. If there are two bridge domains needed, you can configure one bridge domain as VLAN-100 and the other as VLAN-200. However, the configuration requirements are different when implementing service provider style or enterprise style. Here is a look at both styles using the same interfaces and VLANs.

Service provider style involves configuring the values for three main parameters, plus the bridge domains to connect them:

• VLAN tagging—Configure the bridged physical interfaces with vlan-tagging to allow them to operate in IEEE 802.1Q mode, also known as a trunk interface.

• Extended VLAN Bridge—Configure the physical interface with the encapsulation statement type extended-vlan-bridge to allow bridging on each logical interface.

• Logical unit—Configure a logical unit for each bridged VLAN ID. In most cases, you configure the unit number to be the same as the VLAN ID (that is, unit 100 = VLAN ID 100).

• Bridge domains—Configure the VLAN bridge domains to associate the logical interfaces with the correct VLAN IDs.

Here is the service provider style configuration showing two interfaces used for bridging across two bridge domains, VLAN ID 100 and 200.

Note that each physical interface has VLAN tagging enabled as well as extended VLAN bridge encapsulation. There are many more parameters that can be configured in service provider style.

In contrast, enterprise style involves configuring the values for three different parameters, plus the bridge domains to connect them:

• Family— Configure each bridged physical interface with the family type bridge.

• Interface mode—Configure logical interface so that the physical interface operates as either an untagged access port (not shown in this topic) or as an IEEE 801Q trunk.

• VLAN ID—Configure each logical interface with a VLAN ID to determine with which bridge the interface belongs.

• Bridge domain—Configure the VLAN bridge domains to associate with the correct VLAN IDs.

Here is the enterprise style configuration showing the same two interfaces used for bridging across the same two bridge domains, VLAN ID 100 and 200.

In exchange for simplicity, enterprise style does not allow you to configure VLAN tagging options or encapsulation type. You do not create a separate logical interface for each VLAN ID.