Understanding Virtual Channels

You configure a virtual channel to set up queuing, packet scheduling, and accounting rules to be applied to one or more logical interfaces. You must apply then the virtual channel to a particular logical interface.

You also create a list of virtual channels that you can assign to a virtual channel group. To define a virtual channel group that you can assign to a logical interface, include the virtual-channel-groups statement at the [edit class-of-service] hierarchy level.

The virtual-channel-group-name can be any name that you want. The virtual-channel-name must be one of the names that you define at the [edit class-of-service virtual-channels] hierarchy level. You can include multiple virtual channel names in a group.

The scheduler map is required. The map-name must be one of the scheduler maps that you configure at the [edit class-of-service scheduler-maps] hierarchy level. For more information, see Example: Configuring Class-of-Service Schedulers on a Security Device.

The shaping rate is optional. If you configure the shaping rate as a percentage, when the virtual channel is applied to a logical interface, the shaping rate is set to the specified percentage of the interface bandwidth. If you configure a shaper on a virtual channel, the shaper limits the maximum bandwidth transmitted by that virtual channel. Virtual channels without a shaper can use the full logical interface bandwidth. If there are multiple unshaped virtual channels, they share the available logical interface bandwidth equally.

When you apply the virtual channel group to a logical interface, a set of eight queues is created for each of the virtual channels in the group. The scheduler-map statement applies a scheduler to these queues. If you include the shaping-rate statement, a shaper is applied to the entire virtual channel.

You must configure one of the virtual channels in the group to be the default channel. Therefore, the default statement is required in the configuration of one virtual channel per channel group. Any traffic not explicitly directed to a particular channel is transmitted by this default virtual channel.

For the corresponding physical interface, you must also include the per-unit-scheduler statement at the [edit interfaces interface-name] hierarchy level as follows:

The per-unit-scheduler statement enables one set of output queues for each logical interface configured under the physical interface.

When you apply a virtual channel group to a logical interface, the software creates a set of eight queues for each of the virtual channels in the group.

If you apply a virtual channel group to multiple logical interfaces, the software creates a set of eight queues on each logical interface. The virtual channel names listed in the group are used on all the logical interfaces. We recommend specifying the scheduler and shaping rates in the virtual channel configuration in terms of percentages, rather than absolute rates. This allows you to apply the same virtual channel group to logical interfaces that have different bandwidths.

When you apply a virtual channel group to a logical interface, you cannot include the scheduler-map and shaping-rate statements at the [edit class-of-service interfaces interface-name unit logical-unit-number] hierarchy level. In other words, you can configure a scheduler map and a shaping rate on a logical interface, or you can configure virtual channels on the logical interface, but not both.

If you configure multiple logical interfaces on a single physical interface, each logical interface is guaranteed an equal fraction of the physical interface bandwidth as follows:

If one or more logical interfaces do not completely use their allocation, the other logical interfaces share the excess bandwidth equally.

If you configure multiple virtual channels on a logical interface, they are each guaranteed an equal fraction of the logical interface bandwidth as follows:

If you configure a shaper on a virtual channel, the shaper limits the maximum bandwidth transmitted by that virtual channel. Virtual channels without a shaper can use the full logical interface bandwidth. If there are multiple unshaped virtual channels, they share the available logical interface bandwidth equally.