Hybrid OpenFlow Switch
Router Configuration Guide 665
A mix of the two methods can be used to retrieve some flow table statistics from
hardware in real-time while retrieving other statistics from the cache. See the Filter
Policy Statistics section of this guide for more details on ACL cache and ACL
statistics.
When the auxiliary channel is enabled, the switch will set up a dedicated auxiliary
channel for statistics. See OpenFlow Switch Auxiliary Channels for more
information.
Operational Notes:
• Flow table statistics displayed through the CLI debugging tools (tools>dump>open-
flow>of-switch) are read in real-time from hardware. However, to protect the system,
executing CLI debugging tool commands within 5 seconds will return the same
statistics for any flow that had its statistics read from hardware within the last 5
seconds.
• When retrieving flow table statistics at scale, it is recommended to either use bulk
requests, or to pace single entry requests in order to obtain the desired balance
between stats real-time accuracy and CPM activity.
OpenFlow Switch Auxiliary Channels
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 will set 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 given H-OFS switch instance. Auxiliary connections use
the same transport as the main connection. The switch will handle 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 will use the next available auxiliary channel. If none of the auxiliary channels are
available, the main channel will be used.
Auxiliary connections can be enabled or disabled without shutting down the switch.
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