The pod does not respond to the SYN packet.

Environment:

• k8s version v1.22.3
• flannel version: image: docker.io/flannel/flannel:v0.22.3
• flannel configmap:

apiVersion: v1
data:
  cni-conf.json: |
    {
      "name": "cbr0",
      "cniVersion": "0.3.1",
      "plugins": [
        {
          "type": "flannel",
          "delegate": {
            "hairpinMode": true,
            "isDefaultGateway": true
          }
        },
        {
          "type": "portmap",
          "capabilities": {
            "portMappings": true
          }
        }
      ]
    }
  net-conf.json: |
    {
      "Network": "192.244.0.0/16",
      "Backend": {
        "Type": "vxlan"
      }
    }
kind: ConfigMap

Problem:

I added a new node A (a physical machine) to the K8s cluster, while the old node B was a virtual machine. When I was on the new machine A, I used the command "ping" to reach the pod on node B, and it worked fine. However, when I used the curl command, it was abnormal.

Ping test is ok.

Curl test is not ok. This pod is listening on port 80. On other older machines, the curl test can be performed successfully.

This is the package I captured on this pod.

After I executed "netstat -s" in the pod's net ns, I found that these two indicators would increase along with my curl test.

This seems to be a TCP checksum issue. Could you please tell me if there are any relevant solutions?