Description of problem:

container pod cannot receive packets when UDP packet size greater than cluster MTU 

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

4.17.0-0.nightly-2024-09-03-024255 

How reproducible:

always

Steps to Reproduce:

1. setup bm with ovn plugin

2. check cluster mtu
# oc get network.config -oyaml | grep -i mtu
    clusterNetworkMTU: 1400

3. create test pod
# oc get pod -owide -n test-qw
NAME        READY   STATUS    RESTARTS   AGE   IP             NODE                                       NOMINATED NODE   READINESS GATES
hello-pod   1/1     Running   0          21h   10.130.2.120   openshift-qe-029.lab.eng.rdu2.redhat.com   <none>           <none>

4. using ncat to listen one port and send UDP packets 1644 outside cluster (do this on provision server)
# ls -l size_1644 
-rw-r--r--. 1 root root 1644 Sep  4 03:19 size_1644
# ncat -ul 192.168.111.1 1434 < size_1644

5. checking in test pod to see if it can receive the UDP packets
# oc rsh pod/hello-pod
~ $ ncat -u 192.168.111.1 1434
dd
^C

Actual results:

test pod cannot receive the UDP packets

Expected results:

test pod can receive the UDP packets

Additional info:

1. the host can receive the UDP packets
2. test with UDP packet size 1372, both the pod and host can receive the UDP packets

This is an regression issue, previous bug is https://issues.redhat.com/browse/OCPBUGS-18467 

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.

• When showing the results from commands, include the entire command in the output.  
• For OCPBUGS in which the issue has been identified, label with “sbr-triaged”
• For OCPBUGS in which the issue has not been identified and needs Engineering help for root cause, label with “sbr-untriaged”
• Do not set the priority, that is owned by Engineering and will be set when the bug is evaluated
• Note: bugs that do not meet these minimum standards will be closed with label “SDN-Jira-template”
• For guidance on using this template please see
  OCPBUGS Template Training for Networking  components