Figuring TCP segmentation offload
Article ID: 126263
Updated On:
Products
Issue/Introduction
Site had just moved to a z14 with an OSA card at release 6.
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It was believed it would support SEGMENTATIONOFFLOAD in TCP/IP.
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Before deciding upon using TCP segmentation offload support--as NetMaster for TCP/IP performance views has figures for tcpSegmentsSent
(under IP, TCP, and UDP Monitoring)--it was asked how much segmenting of packets was going on. Or: How many of these
segments were segmented by TCP/IP as opposed to it fitting a complete packet into one segment.
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Environment
OS: z/OS.
Cause
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Resolution
We 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 ifOutPktsTCPSegOff (Outbound TCP pkts requesting seg offload). (PF04 can
be used to add more selectable attributes.) Later the site explained positively that the suggested monitoring
caused figures to start showing on the OSA display screen.
Notes:
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.
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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.
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Additional Information
TCP segmentation offload page documentation at IBM: TCP segmentation offload .
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