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Status Not under consideration
Workspace z/OS
Created by Guest
Created on Dec 23, 2019

DupAck - Input and Output Out-of-order packets

It was noticed an abnormal ammount of "Dup acks" in TCP connections. Since the two end points of
those connections are inside a datacenter (no external links) it usually means there are lost packets.
Some traces (SYSTCPDA and SYSTCPOT) were captured and it was verified there were outgoing packets marked as out of order. As result we have not only dup acks but also TCP retransmissions.

SYSTCPDA and SYSTCPOT traces shows TCP packets leave the tcpip stack in order but when they leave the OSA they get out of order. It happens with or without SEGMENTATIONOFFLOAD coded in tcpip stack profile.
The same behavior was noticed for inbound packets, ie, they arrive in order in OSA (SYSTCPOT) but they are shown as ooo in tcpip stack (SYSTCPDA).

Idea priority High
  • Guest
    Reply
    |
    Aug 12, 2022
    IWQ addresses this issue by eliminating out-of-order inbound packets.