Control Plane
The control plane of a port extension system is responsible for control channel and internal forwarding channel.
Control Channel
In a port extension system, a control channel is established between an AP and master. As shown in Figure 3-3, through the control channel:
The master delivers forwarding entries to the AP, implementing data transmission between the master and AP.
The AP reports to the master an external communication interface's attributes (including the physical and protocol states, MAC address, and bandwidth of the interface). The attributes can be queried on the corresponding port extension interface on the master.
Internal Forwarding Channel
An internal forwarding channel must be established for a port extension system to forward service traffic. An internal forwarding channel is established through configuration. On the network shown in Figure 3-4, bind the internal communication interfaces of the master and AP, and then bind the master's internal communication interface and the AP's external communication interface. After the configuration is complete, the master creates a port extension interface for the AP's external communication interface. The system establishes a bidirectional channel along the path: AP's external communication interface -> AP's internal communication interface -> master's internal communication interface -> master's port extension interface. The system automatically allocates a label (called the NVTAG) to the channel. Packets transmitted within the channel carry the NVTAG for packet identification.
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