HP OpenFlow 1.3 Administrator Guide Wired Switches K/KA/KB/WB 15.15

B Implementation notes
This section documents some of the behaviors exhibited during the implementation of OpenFlow.
These behaviors were exposed during testing and may include unit, conformance, integration,
interoperability, stress and system testing.
A hardware flow with an idle timeout of 10 seconds gets deleted even
though packets match the flow within the idle timeout
Problem statement
A hardware rule is programmed with idle timeout as 10 seconds and hard timeout
as 0. Packets are pumped at 1000 pps to the switch matching the flow. However,
after 10 seconds, the rule gets removed from the switch.
Reason for this behavior
By default the hardware statistics refresh rate (set using openflow
hardware statistics refresh rate and information available through
show openflow) is 20 seconds. This means that the packet count statistics get
updated only every 20 seconds. So, when the idle timeout is set to less than 20
seconds, when a check is done for flow statistics after 10 seconds, it would not be
updated. Hence, the flow would get deleted.
Customer Note
The user has the option of reducing or incriminating the refresh rate. However, the
user needs to be aware of its implications. An increase in refresh rate would lead
to deletion of flows which has an idle timeout less than the configured refresh rate.
A decrease in refresh rate would lead to over‐use of CPU (because of polling
hardware statistics more frequently.)
Controller flows — flow in hardware and processing software
Flows with an action to send matching traffic to controller are actually installed on hardware. But,
the actual traffic forwarding takes place in software as we need to add the required OpenFlow
specific headers. Due to this characteristic, the actual forwarding will not take place at the line
rate. A sample controller flow would look like:
Example
In this example, any packet that comes on port A1, will be forwarded to the
controller after adding required OpenFlow packet headers (as the packet will be
sent as a packet_in) to the controller. Since this processing is done on software, we
will not be able to send the incoming traffic at line rate.
HP-8206zl(openflow)# show openflow instance test flows
Flow 1
Incoming Port : A1 Ethernet Type : 0x0000
Source MAC : 000000-000000 Destination MAC :
000000-000000
VLAN ID : 0 VLAN priority :
Source IP : 0.0.0.0 Destination IP : 0.0.0.0
IP Protocol : 0 IP ToS Bits : 0
Source Port : 0 Destination Port : 0
Priority : 2
Duration : 1 seconds
Idle Timeout : 60 seconds Hard Timeout : 0 seconds
Packet Count : 1 Byte Count : 0
Flow Location : Hardware
72 Implementation notes