H3C Technologies H3C S6800 Series Switches - Manual (Page 15)

7
• Asynchronous-Configuration—These are used by the controller to set an additional filter on the
asynchronous messages that it wants to receive, or to query that filter. It is typically used when the
switch connects to multiple controllers.
Asynchronous messages
Switches send asynchronous messages to controllers to inform a packet arrival or switch state change. For
example, when a flow entry is removed due to timeout, the switch sends a flow-removed message to
inform the controller.
The asynchronous messages include the following subtypes:
• Packet-In—Transfer the control of a packet to the controller. For all packets forwarded to the
Controller reserved port using a flow entry or the table-miss flow entry, a packet-in event is always
sent to controllers. Other processing, such as TTL checking, can also generate packet-in events to
send packets to the controller. The packet-in events can include the full packet or can be configured
to buffer packets in the switch. If the packet-in event is configured to buffer packets, the packet-in
events contain only some fraction of the packet header and a buffer ID. The controller processes the
full packet or the combination of the packet header and the buffer ID. Then, the controller sends a
packet-out message to direct the switch to process the packet.
• Flow-Removed—Inform the controller about the removal of a flow entry from a flow table. These are
generated due to a controller flow delete request or the switch flow expiry process when one of the
flow timeouts is exceeded.
• Port-status—Inform the controller of a state or setting change on a port.
• Error—Inform the controller of a problem or error.
Symmetric messages
Symmetric messages are sent without solicitation, in either direction.
The symmetric messages contain the following subtypes:
• Hello—Hello messages are exchanged between the switch and controller upon connection startup.
• Echo—Echo request or reply messages can be sent from either the switch or the controller, and must
return an echo reply. They are mainly used to verify the liveness of a controller-switch connection,
and might also be used to measure its latency or bandwidth.
• Experimenter—This is a staging area for features meant for future OpenFlow revisions.
Protocols and standards
OpenFlow Switch Specification Version 1.3.1