I am testing my DNS Service and following the guide from link : Debugging DNS Resolution - Kubernetes
As per the steps, I have created a pod busybox and then executed the command which tests the DNS service. But I am getting the following error.
kubi@kubem:~/wordpress2$ kubectl exec -ti busybox -- nslookup kubernetes.default
Server: 10.96.0.10
Address 1: 10.96.0.10
nslookup: can't resolve 'kubernetes.default'
command terminated with exit code 1
kubi@kubem:~/wordpress2$ kubectl exec busybox cat /etc/resolv.conf
nameserver 10.96.0.10
search default.svc.cluster.local svc.cluster.local cluster.local lan
options ndots:5
Please help me to investigate this further. My kube-system pods are in running state.
Here is the PODs I am running on the system with all other parameters 
kubi@kubem:~/wordpress2$ kubectl get all -o wide -n kube-system
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
pod/coredns-86c58d9df4-dxr5l 1/1 Running 92 12d 10.244.0.37 kubem <none> <none>
pod/coredns-86c58d9df4-xc4gg 1/1 Running 94 12d 10.244.0.39 kubem <none> <none>
pod/etcd-kubem 1/1 Running 12 12d 192.168.56.110 kubem <none> <none>
pod/kube-apiserver-kubem 1/1 Running 99 12d 192.168.56.110 kubem <none> <none>
pod/kube-controller-manager-kubem 1/1 Running 122 12d 192.168.56.110 kubem <none> <none>
pod/kube-flannel-ds-amd64-bpkhg 1/1 Running 7 12d 192.168.56.112 kubew2 <none> <none>
pod/kube-flannel-ds-amd64-j2ww9 1/1 Running 8 12d 192.168.56.111 kubew1 <none> <none>
pod/kube-flannel-ds-amd64-v5hb2 1/1 Running 15 12d 192.168.56.110 kubem <none> <none>
pod/kube-proxy-f697j 1/1 Running 7 12d 192.168.56.111 kubew1 <none> <none>
pod/kube-proxy-sbsfv 1/1 Running 12 12d 192.168.56.110 kubem <none> <none>
pod/kube-proxy-v5k4p 1/1 Running 7 12d 192.168.56.112 kubew2 <none> <none>
pod/kube-scheduler-kubem 1/1 Running 143 12d 192.168.56.110 kubem <none> <none>
pod/kubernetes-dashboard-57df4db6b-xgnsx 1/1 Running 110 12d 10.244.0.38 kubem <none> <none>
pod/tiller-deploy-dbb85cb99-7nr2l 1/1 Running 7 12d 10.244.2.51 kubew2 <none> <none>
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE SELECTOR
service/kube-dns ClusterIP 10.96.0.10 <none> 53/UDP,53/TCP 12d k8s-app=kube-dns
service/kubernetes-dashboard ClusterIP 10.104.199.119 <none> 443/TCP 12d k8s-app=kubernetes-dashboard
service/prom-prometheus-operator-kube-controller-manager ClusterIP None <none> 10252/TCP 7d23h k8s-app=kube-controller-manager
service/prom-prometheus-operator-kube-dns ClusterIP None <none> 10054/TCP,10055/TCP 7d23h k8s-app=kube-dns
service/prom-prometheus-operator-kube-etcd ClusterIP None <none> 4001/TCP 7d23h k8s-app=etcd-server
service/prom-prometheus-operator-kube-scheduler ClusterIP None <none> 10251/TCP 7d23h k8s-app=kube-scheduler
service/prom-prometheus-operator-kubelet ClusterIP None <none> 10250/TCP 7d23h <none>
service/tiller-deploy ClusterIP 10.107.118.136 <none> 44134/TCP 12d app=helm,name=tiller
NAME DESIRED CURRENT READY UP-TO-DATE AVAILABLE NODE SELECTOR AGE CONTAINERS IMAGES SELECTOR
daemonset.apps/kube-flannel-ds-amd64 3 3 3 3 3 beta.kubernetes.io/arch=amd64 12d kube-flannel quay.io/coreos/flannel:v0.11.0-amd64 app=flannel,tier=node
daemonset.apps/kube-flannel-ds-arm 0 0 0 0 0 beta.kubernetes.io/arch=arm 12d kube-flannel quay.io/coreos/flannel:v0.11.0-arm app=flannel,tier=node
daemonset.apps/kube-flannel-ds-arm64 0 0 0 0 0 beta.kubernetes.io/arch=arm64 12d kube-flannel quay.io/coreos/flannel:v0.11.0-arm64 app=flannel,tier=node
daemonset.apps/kube-flannel-ds-ppc64le 0 0 0 0 0 beta.kubernetes.io/arch=ppc64le 12d kube-flannel quay.io/coreos/flannel:v0.11.0-ppc64le app=flannel,tier=node
daemonset.apps/kube-flannel-ds-s390x 0 0 0 0 0 beta.kubernetes.io/arch=s390x 12d kube-flannel quay.io/coreos/flannel:v0.11.0-s390x app=flannel,tier=node
daemonset.apps/kube-proxy 3 3 3 3 3 <none> 12d kube-proxy k8s.gcr.io/kube-proxy:v1.13.3 k8s-app=kube-proxy
NAME READY UP-TO-DATE AVAILABLE AGE CONTAINERS IMAGES SELECTOR
deployment.apps/coredns 2/2 2 2 12d coredns k8s.gcr.io/coredns:1.2.6 k8s-app=kube-dns
deployment.apps/kubernetes-dashboard 1/1 1 1 12d kubernetes-dashboard k8s.gcr.io/kubernetes-dashboard-amd64:v1.10.1 k8s-app=kubernetes-dashboard
deployment.apps/tiller-deploy 1/1 1 1 12d tiller gcr.io/kubernetes-helm/tiller:v2.12.3 app=helm,name=tiller
NAME DESIRED CURRENT READY AGE CONTAINERS IMAGES SELECTOR
replicaset.apps/coredns-86c58d9df4 2 2 2 12d coredns k8s.gcr.io/coredns:1.2.6 k8s-app=kube-dns,pod-template-hash=86c58d9df4
replicaset.apps/kubernetes-dashboard-57df4db6b 1 1 1 12d kubernetes-dashboard k8s.gcr.io/kubernetes-dashboard-amd64:v1.10.1 k8s-app=kubernetes-dashboard,pod-template-hash=57df4db6b
replicaset.apps/tiller-deploy-69ffbf64bc 0 0 0 12d tiller gcr.io/kubernetes-helm/tiller:v2.12.3 app=helm,name=tiller,pod-template-hash=69ffbf64bc
replicaset.apps/tiller-deploy-dbb85cb99 1 1 1 12d tiller gcr.io/kubernetes-helm/tiller:v2.12.3 app=helm,name=tiller,pod-template-hash=dbb85cb99
kubi@kubem:~/wordpress2$
Here are the logs for both coredns pods :
kubi@kubem:~/wordpress2$ kubectl logs -f coredns-86c58d9df4-dxr5l -n kube-system
.:53
2019-03-12T08:37:33.029Z [INFO] CoreDNS-1.2.6
2019-03-12T08:37:33.029Z [INFO] linux/amd64, go1.11.2, 756749c
CoreDNS-1.2.6
linux/amd64, go1.11.2, 756749c
[INFO] plugin/reload: Running configuration MD5 = f65c4821c8a9b7b5eb30fa4fbc167769
kubi@kubem:~/wordpress2$ kubectl logs -f coredns-86c58d9df4-xc4gg -n kube-system
.:53
2019-03-12T08:37:35.359Z [INFO] CoreDNS-1.2.6
2019-03-12T08:37:35.359Z [INFO] linux/amd64, go1.11.2, 756749c
CoreDNS-1.2.6
linux/amd64, go1.11.2, 756749c
[INFO] plugin/reload: Running configuration MD5 = f65c4821c8a9b7b5eb30fa4fbc167769
Kubectl Version:
kubi@kubem:~/wordpress2$ kubectl version
Client Version: version.Info{Major:"1", Minor:"13", GitVersion:"v1.13.3", GitCommit:"721bfa751924da8d1680787490c54b9179b1fed0", GitTreeState:"clean", BuildDate:"2019-02-01T20:08:12Z", GoVersion:"go1.11.5", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"13", GitVersion:"v1.13.3", GitCommit:"721bfa751924da8d1680787490c54b9179b1fed0", GitTreeState:"clean", BuildDate:"2019-02-01T20:00:57Z", GoVersion:"go1.11.5", Compiler:"gc", Platform:"linux/amd64"}