FIGURING TCP SEGMENTATION

Document ID : KB000126263
Last Modified Date : 05/02/2019
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Issue:

Cust explained that they had just moved to a z14 with an OSA card at
release 6.

They believe it would support SEGMENTATIONOFFLOAD in TCP/IP.

Before deciding upon using TCP segmentation offload support they
wanted to know--as NetMaster for TCP/IP performance views has
figures for tcpSegmentsSent (under IP, TCP, and UDP Monitor-
ing)--how much segmenting of packets was going on. Or: How
many of these segments were segmented by TCP/IP as op-
posed to it fitting a complete packet into one segment.

Environment:
OS: z/OS.
Resolution:

NM L2 Support suggested this other monitoring:

In /IPMON: UM command in front of stack name: U command in front of
Network Interface Monitoring:  Update attributes ifOutPktsTCPSegGen
(Outbound TCP pkts generated by seg offload) and ifOutPktsTCP-
SegOff (Outbound TCP pkts requesting seg offload). (PF04 can
be used to add more selectable attributes.)

Later cust explained--positively--that the NM L2 suggested monitoring
caused figures to start showing on the OSA display screen.

Note from NM L2:

There is no requirement to set alerts for any attribute. Whatever alerting
is seen is out of the box. NetMaster collects the data for performance
viewing purposes. It is the user’s choice if he or she just wants
statistical gathering--or monitoring and alerting based upon
that monitoring.

Note from NM L2:

Once the user adds an attribute it takes a full hour to be able to see
summary data and a full day to see daily data--and so forth. One
can view the current up-to-the-minute samples by using
S=Samples.

Additional Information:

TCP segmentation offload page:
 
https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.3.0/com.ibm.zos.v2r3.halz002/ip_tcp_segmentation_offload.htm