Shadow Node Overview

The frame forwarding ASIC (FFA) and the 10-Gigabit Ethernet forwarding ASIC (TFA) require that all queues be above the port scheduler node with two additional scheduler nodes. The router implicitly creates phantom nodes when you do not specify two scheduler nodes above the port interface. Phantom nodes cannot be monitored using show commands.

Phantom nodes have the same weight as the associated queues and are not shaped, which preserves the behavior of the queues as if they are at their original level.

Figure 1 compares a scheduler hierarchy with and without phantom nodes.

Figure 1: Phantom Nodes

The first scheduler hierarchy displayed in Figure 1 shows Queue A, Queue B, and Node C at the same scheduler level and with the same weight of 8. They equally share the bandwidth available to the level 1 node.

The second scheduler hierarchy in Figure 1 shows the phantom nodes the router added for Queue A and Queue B. It also shows the weight associated with Queue A and Queue B. As the result, Phantom A, Phantom B, and Node C share the bandwidth of the level 1 node. The phantom nodes do not change the behavior of Queue A and Queue B.