Flow Offload
============

cento has been designed to process high-speed traffic with moderate CPU load.
Traffic processing can be further optimized by offloading flows to the adapter, on Napatech adapters
featuring an hardware Flow Manager. This dramatically reduces the load on the CPU.
Cento offloads flows to the adapter as soon as the application protocol has been detected (this
requires a few packets for each flow, depending on the actual protocol).

Note: a Flow Manager enabled firmware is required in order to use flow offload on the adapter.

FlowPeriodicStatisticsProfiles needs to be configured in the adapter to deliver periodic flow updates.
Example (snippet from /opt/napatech3/config/ntservice.ini):

.. code-block:: text

   FlowPeriodicStatisticsProfiles = [0,0,10000000000],[0,0,0],[0,0,0],[0,0,0],[0,0,0],[0,0,0],[0,0,0]

Please find below a sample "flow-offload.ntpl" script that can be used to configure one (or more) stream.

.. code-block:: text

   Delete = All
   
   // Pair of uplink and downlink ports
   Define UL_PORT = Macro("0")
   Define DL_PORT = Macro("1")
   
   // Streams / threads
   Define STREAMS = Macro("(0..0)")
   Define NUMA    = Macro("0")
   
   Define TX_FORWARD = Macro("0x00")
   Define TX_DISCARD = Macro("0x08")
   
   Define FLM_HIT       = Macro("0x00")
   Define FLM_MISS      = Macro("0x10")
   Define FLM_UNHANDLED = Macro("0x20")
   
   Define FLM_DISCARD = Macro("3")
   Define FLM_FORWARD = Macro("4")
   
   Define isIPv4    = Macro("Layer3Protocol==IPv4")
   Define isTcpUdp  = Macro("Layer4Protocol==TCP,UDP")
   
   KeyType[Name=KT_4Tuple] = {32, 32, 16, 16}
   
   Define KeyDefProtoSpec = Macro("(Layer3Header[12]/32, Layer3Header[16]/32, Layer4Header[0]/16, Layer4Header[2]/16)")
   KeyDef[Name=KD_4Tuple; KeyType=KT_4Tuple; IpProtocolField=Outer; KeySort=Sorted] = KeyDefProtoSpec
   
   HashMode = Hash5TupleSorted
   
   Setup[NUMANode=NUMA] = StreamId == STREAMS
   
   // Tx port number is the first 3 bits of the NtDyn1Descr_s->color at offset 138 (0b000XXX)
   // Tx forward/discard verdict is bit 4 of the NtDyn1Descr_s->color at offset 141 (0b00X000)
   Setup[TxDescriptor=DYN; TxPorts=UL_PORT,DL_PORT; TxPortPos=138; TxIgnorePos=141] = StreamId==STREAMS
   
   // Set TX port value, which is the first 3 bits of the NtDyn1Descr_s->color
   Assign[ColorMask=DL_PORT; Descriptor=DYN1] = Port==UL_PORT
   Assign[ColorMask=UL_PORT; Descriptor=DYN1] = Port==DL_PORT
   
   // Set TX forward/discard, which is bit 4 of the NtDyn1Descr_s->color
   Assign[ColorMask=TX_FORWARD; Descriptor=DYN1] = Port==UL_PORT,DL_PORT
   
   // New and unhandled flows are sent to the host
   Assign[StreamId=STREAMS; ColorMask=FLM_UNHANDLED; Descriptor=DYN1] = Port==UL_PORT,DL_PORT AND isIPv4 AND isTcpUdp AND Key(KD_4Tuple, KeyID=1) == UNHANDLED
   Assign[StreamId=STREAMS; ColorMask=FLM_MISS;      Descriptor=DYN1] = Port==UL_PORT,DL_PORT AND isIPv4 AND isTcpUdp AND Key(KD_4Tuple, KeyID=1) == MISS
   
   // Drop discarded flows
   Assign[StreamId=DROP] = Port==UL_PORT,DL_PORT AND isIPv4 AND isTcpUdp AND Key(KD_4Tuple, KeyID=1) == FLM_DISCARD
   
   // Forward allowed flows between ports
   Assign[StreamId=Drop; DestinationPort=DL_PORT] = Port==UL_PORT AND isIPv4 AND isTcpUdp AND Key(KD_4Tuple, KeyID=1) == FLM_FORWARD
   Assign[StreamId=Drop; DestinationPort=UL_PORT] = Port==DL_PORT AND isIPv4 AND isTcpUdp AND Key(KD_4Tuple, KeyID=1) == FLM_FORWARD

Command to load the NTPL script to the adapter:

.. code-block:: bash

   sudo /opt/napatech3/bin/ntpl -f flow-offload.ntpl

In order to enable flow offload in nProbe Cento, a :code:`--flow-offload` option is available. Example:

.. code-block:: bash

   cento-bridge -i nt:stream0 --flow-offload --dpi-level 2