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Virtual Channels Overview


You can configure virtual channels to limit traffic sent from a corporate headquarters to its branch offices. Virtual channels might be required when the headquarters site has an expected aggregate bandwidth higher than that of the individual branch offices. The headquarters router must limit the traffic sent to each branch office router to avoid oversubscribing their links. For instance, if branch 1 has a 1.5 Mbps link and the headquarters router attempts to send 6 Mbps to branch 1, all of the traffic in excess of 1.5-Mbps is dropped in the ISP network.

You configure virtual channels on a logical interface. Each virtual channel has a set of eight queues with a scheduler and an optional shaper. You can use an output firewall filter to direct traffic to a particular virtual channel. For example, a filter can direct all traffic with a destination address for branch office 1 to virtual channel 1, and all traffic with a destination address for branch office 2 to virtual channel 2.

Although a virtual channel group is assigned to a logical interface, a virtual channel is quite different from a logical interface. The only features supported on a virtual channel are queuing, packet scheduling, and accounting. Rewrite rules and routing protocols apply to the entire logical interface.

When you configure virtual channels on an interface, the virtual channel group uses the same scheduler and shaper you configure at the [edit interfaces interface-name unit logical-unit-number] hierarchy level. In this way, virtual channels are an extension of regular scheduling and shaping and are not independent entities.