Description of problem: A traffic listener pod is created and exposed via service type NodePort. Traffic is sent from client pod to the exposed nodeport on all Nodes IPs one by one. All other nodes shows UNREPLIED entry in conntrack table except the one client pod runs on (from where the traffic is sent). Client pod is just a ping pod utilized to send traffic. 

All nodes supposed to be proxying the exposed service due to type NodePort.

$ oc get pods
NAME                READY   STATUS    RESTARTS   AGE
hello-pod           1/1     Running   0          22h  <<<<Ping pod
udp-rc-lcbst        1/1     Running   0          51m  <<<<Traffic listener pod

$ oc get svc
NAME           TYPE       CLUSTER-IP       EXTERNAL-IP   PORT(S)          AGE
udp-rc-lcbst   NodePort   172.30.154.219   <none>        8080:31963/UDP   105m


$ sudo podman run -rm --network host --privileged docker.io/aosqe/conntrack-tool conntrack -L | grep 31963
udp      17 5 src=172.31.130.146 dst=172.31.139.127 sport=34999 dport=31963 [UNREPLIED] src=172.31.139.127 dst=172.31.130.146 sport=31963 dport=34999 mark=0 secctx=system_u:object_r:unlabeled_t:s0 use=1
udp      17 12 src=172.31.130.146 dst=172.31.159.254 sport=52167 dport=31963 [UNREPLIED] src=172.31.159.254 dst=172.31.130.146 sport=31963 dport=52167 mark=0 secctx=system_u:object_r:unlabeled_t:s0 use=1
udp      17 20 src=172.31.130.146 dst=172.128.159.64 sport=37556 dport=31963 [UNREPLIED] src=172.128.159.64 dst=172.31.130.146 sport=31963 dport=37556 mark=0 secctx=system_u:object_r:unlabeled_t:s0 use=1
udp      17 149 src=172.31.130.146 dst=172.31.130.146 sport=58178 dport=31963 src=10.129.2.23 dst=10.128.2.1 sport=8080 dport=58178 [ASSURED] mark=0 secctx=system_u:object_r:unlabeled_t:s0 use=1

sudo podman command is just running conntrack utility in a container and removes container post command execution

Version-Release number of selected component (if applicable): 4.0.0-0.nightly-2019-04-05-165550

$ oc version --short
Client Version: v4.0.22
Server Version: v1.13.4+ab11434


How reproducible: Always

Steps to Reproduce:
1. Create traffic listener pod and a ping pod. See in addtional info below
2. oc expose pod <traffic_listener_pod> --type=NodePort --port=8080 --protocol=UDP
3. Send traffic via client pod to all node IPs and nodeport one by one

Actual results: Not all nodes are responding to client but only that node on with client on 

Expected results: Expecting all nodes to reply to client as the service type is NodePort which is supposed to expose service on all nodes

Additional info: 

traffic listener pod template
-----------------------------

{
    "apiVersion": "v1",
    "kind": "List",
    "items": [
        {
            "apiVersion": "v1",
            "kind": "ReplicationController",
            "metadata": {
                "labels": {
                    "name": "udp-rc"
                },
                "name": "udp-rc"
            },
            "spec": {
                "replicas": 1,
                "template": {
                    "metadata": {
                        "labels": {
                            "name": "udp-pods"
                        }
                    },
                    "spec": {
                        "containers": [
                            {
                              "command": [ "/usr/bin/ncat", "-u", "-l", "8080","--keep-open", "--exec", "/bin/cat"],
                              "name": "udp-pod",
                              "image": "aosqe/pod-for-ping"
                            }
                        ],
                 "restartPolicy": "Always"
                    }
                }
            }
       }
    ]
}


$ oc get svc -oyaml
-----------------------
apiVersion: v1
items:
- apiVersion: v1
  kind: Service
  metadata:
    creationTimestamp: 2019-04-09T18:02:22Z
    labels:
      name: udp-pods
    name: udp-rc-lcbst
    namespace: test
    resourceVersion: "880960"
    selfLink: /api/v1/namespaces/test/services/udp-rc-lcbst
    uid: 9fddbc9b-5af1-11e9-82b2-02302f122dd4
  spec:
    clusterIP: 172.30.154.219
    externalTrafficPolicy: Cluster
    ports:
    - nodePort: 31963
      port: 8080
      protocol: UDP
      targetPort: 8080
    selector:
      name: udp-pods
    sessionAffinity: None
    type: NodePort
  status:
    loadBalancer: {}
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""