The H-OFS supports auxiliary channels, as defined in OpenFlow version 1.3.1. The packet-in and statistics functions are supported on the auxiliary channels as well as on the main channel.
When the auxiliary channel is enabled on a switch (using the aux-channel-enable command), the switch sets up a dedicated auxiliary channel for statistics (Auxiliary ID 1) and a dedicated auxiliary channel for packet-in (Auxiliary ID 2) if a packet-in action is configured, to every controller for a specific H-OFS switch instance. Auxiliary connections use the same transport as the main connection. The switch handles any requests over any established channel and respond on the same channel even if a specific requested auxiliary channel is available.
The H-OFS instance uses the packet-in connection for packet-in functionality by default and expects (but does not require) the controller to use the statistics channel for statistics processing by default.
The switch uses the auxiliary channels (packet-in for packet-in-specific requests and statistics for statistics-specific requests) as long as they are available. If they are not available, the switch uses the next available auxiliary channel. If none of the auxiliary channels are available, the main channel is used.
Auxiliary connections can be enabled or disabled without shutting down the switch.