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  1. OpenShift Bugs
  2. OCPBUGS-11266

[4.12.4] Larger packet size than MTU causes packet drops

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    Description

      Description of problem:

      Larger packet size than MTU causes packet drops observed. This is reproducible when we have TCP segment size is larger than negotiated MSS which is kicked in TSO. 
      
      Test Result(Page 34) - CASE 2-4 - OVN - Pod to Pod in different nodes(Slide Page 34)
      TCP Test - "without Packet length option."
      +--------------+----------+
      | Packets/sec* | TCP Retr |
      +--------------+----------+
      | 5,800        | 3        |
      | 5,800        | 216      |
      | 5,800        | 121      |
      +--------------+----------+ 
      ** https://docs.google.com/presentation/d/1HbSAvuIf4gf0NGZyu59EawUHXSopVr2PKNA-T9bvC40/edit?usp=sharing
      
      Negotiated MSS 8340, but TCP segment size larger than 58Kbytes(TSO kicks in). 
      
      **Noted - this would be a minor contribution for packet drop because cluster MTU is big enough(pMTU 8500) for vCU cluster. 
      
      
      

      Version-Release number of selected component (if applicable):

      [root@bastion ~]# oc get clusterversions.config.openshift.io 
      NAME      VERSION   AVAILABLE   PROGRESSING   SINCE   STATUS
      version   4.12.4    True        False         10d     Cluster version is 4.12.4
      [root@bastion ~]# 

      How reproducible:

      iperf3 commands
      
      1. bring up iPerf3 Server - iperf3 -s -p 60001
      2. bring and client and issue the command - iperf3 -c 2001:feed:beef::301 -p 60001 -P 64 -b 30M -N -t 100 -V

      Steps to Reproduce:

      Same as how reproducible.
      

      Actual results:

       

      Expected results:

      No TCP transmission even TSO kicks in.

      Additional info:

       

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              mcambria Michael Cambria
              soh@redhat.com Sehee Oh
              Anurag Saxena Anurag Saxena
              Inho Cho, Ryan Taeryoung Hur
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                Updated:
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