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  1. OpenShift Bugs
  2. OCPBUGS-58288

[4.18] br-ex has cluster network MTU cached on OCP nodes causing traffic outage.

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      * Before this update, certain traffic patterns with large packets running between {product-title} nodes and pods triggered an {product-title} host to send Internet Control Message Protocol (ICMP) needs frag to another {product-title} host. This situation lowered the viable maximum transmission unit (MTU) in the cluster. As a consequence, executing the `ip route show cache` command displayed a cached route with a lower MTU than the physical link. Packets were dropped and {product-title} components were degrading because the host did not send pod-to-pod traffic with the large packets. With this release, NF Tables rules prevent the {product-title} nodes from lowering their MTU in response to these traffic patterns. (link:https://issues.redhat.com/browse/OCPBUGS-58288[OCPBUGS-58288])
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      * Before this update, certain traffic patterns with large packets running between {product-title} nodes and pods triggered an {product-title} host to send Internet Control Message Protocol (ICMP) needs frag to another {product-title} host. This situation lowered the viable maximum transmission unit (MTU) in the cluster. As a consequence, executing the `ip route show cache` command displayed a cached route with a lower MTU than the physical link. Packets were dropped and {product-title} components were degrading because the host did not send pod-to-pod traffic with the large packets. With this release, NF Tables rules prevent the {product-title} nodes from lowering their MTU in response to these traffic patterns. (link: https://issues.redhat.com/browse/OCPBUGS-58288 [ OCPBUGS-58288 ])
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      Description of problem:
      We are still seeing the br-ex route having cluster network MTU cached
      This was suppose to be resolved with https://issues.redhat.com/browse/OCPBUGS-24350
      in 4.14.7
      ref : https://access.redhat.com/solutions/7048134
      https://access.redhat.com/errata/RHSA-2023:7831
      but still seen in OCP 4.14.28

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

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      Please fill in the following template while reporting a bug and provide as much relevant information as possible. Doing so will give us the best chance to find a prompt resolution.

      Affected Platforms:

      Is it an

      1. internal CI failure
      2. customer issue / SD
      3. internal RedHat testing failure

      If it is an internal RedHat testing failure:

      • Please share a kubeconfig or creds to a live cluster for the assignee to debug/troubleshoot along with reproducer steps (specially if it's a telco use case like ICNI, secondary bridges or BM+kubevirt).

      If it is a CI failure:

      • Did it happen in different CI lanes? If so please provide links to multiple failures with the same error instance
      • Did it happen in both sdn and ovn jobs? If so please provide links to multiple failures with the same error instance
      • Did it happen in other platforms (e.g. aws, azure, gcp, baremetal etc) ? If so please provide links to multiple failures with the same error instance
      • When did the failure start happening? Please provide the UTC timestamp of the networking outage window from a sample failure run
      • If it's a connectivity issue,
      • What is the srcNode, srcIP and srcNamespace and srcPodName?
      • What is the dstNode, dstIP and dstNamespace and dstPodName?
      • What is the traffic path? (examples: pod2pod? pod2external?, pod2svc? pod2Node? etc)

      If it is a customer / SD issue:

      • Provide enough information in the bug description that Engineering doesn’t need to read the entire case history.
      • Don’t presume that Engineering has access to Salesforce.
      • Do presume that Engineering will access attachments through supportshell.
      • Describe what each relevant attachment is intended to demonstrate (failed pods, log errors, OVS issues, etc).
      • Referring to the attached must-gather, sosreport or other attachment, please provide the following details:
        • If the issue is in a customer namespace then provide a namespace inspect.
        • If it is a connectivity issue:
          • What is the srcNode, srcNamespace, srcPodName and srcPodIP?
          • What is the dstNode, dstNamespace, dstPodName and dstPodIP?
          • What is the traffic path? (examples: pod2pod? pod2external?, pod2svc? pod2Node? etc)
          • Please provide the UTC timestamp networking outage window from must-gather
          • Please provide tcpdump pcaps taken during the outage filtered based on the above provided src/dst IPs
        • If it is not a connectivity issue:
          • Describe the steps taken so far to analyze the logs from networking components (cluster-network-operator, OVNK, SDN, openvswitch, ovs-configure etc) and the actual component where the issue was seen based on the attached must-gather. Please attach snippets of relevant logs around the window when problem has happened if any.
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        OCPBUGS Template Training for Networking  components

              jluhrsen Jamo Luhrsen
              rhn-support-manyayad Mahesh Nyayadhish
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              Weibin Liang Weibin Liang
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                Created:
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