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Table Of Contents
1648 OpenFlow
To accommodate the scenario where the Flow Controller removes many flows
and quickly adds many new flows, the OpenFlow flow database is twice the
size of the hardware database. The extra headroom provides enough space to
buffer the new flows before the old flows are removed from the hardware.
If the OpenFlow Controller adds a flow with the same match criteria as an
existing flow, Dell EMC Networking OpenFlow Hybrid treats the new flow as
a flow modification action. The old flow is deleted from the hardware and the
new flow is added to the hardware.
If a flow cannot be added to the hardware because the hardware reports that it
is out of space, Dell EMC Networking OpenFlow Hybrid sends a message to
the OpenFlow controller indicating that the flow addition failed and removes
the flow from the software table.
Each time the switch fails to add a flow to the hardware, it sends a syslog
message indicating the flow XID.
The switch cannot always accommodate a flow in the hardware because the
hardware space is shared between different flow types and is shared with other
Dell EMC Networking OpenFlow Hybrid components, and because the
hardware usage depends on the flow match criteria.
An example of resource sharing among different flow types is the OpenFlow
1.0 Rule Table (24) and MAC Forwarding Table (25) that share IFP resources.
Different flow types may require a different number of IFP slices. VFP-based
flows (Source MAC VLAN Assignment (4)) have no common resources with
IFP-based flows.
An example of resource sharing between components is the IFP. Both the QoS
component and the OpenFlow component use IFP resources. The system
does not reserve space in the IFP, but instead allocates resources as they are
requested by the application.
The flow match criteria can affect hardware usage in a couple of ways. For
entries that are added to the IFP or the VFP, the hardware table usage on
multi-ASIC switches depends on the port match criteria in the flow. If the
flow matches a physical port, the flow is inserted only into the IFP/VFP on
the ASIC where the physical port is located. If the flow does not match a
specific physical port, the flow is inserted in all ASICs. Since many flows use
the ingress port as a match criterion, the overall flow table capacity depends
on how the flows are distributed across the multiple ASICs.