title: Can't resolve dns from inside k8s pod
body: <p>In dnsutils pod exec <code>ping stackoverflow.com</code></p>
  <pre><code>/ # ping stackoverflow.com
  ping: bad address 'stackoverflow.com'
  </code></pre>
  <p>The <code>/etc/resolve.conf</code> file looks fine from inside the pod</p>
  <pre><code>/ # cat /etc/resolv.conf 
  nameserver 10.96.0.10
  search weika.svc.cluster.local svc.cluster.local cluster.local
  options ndots:5
  </code></pre>
  <p><code>10.96.0.10</code> is the kube-dns service ip:</p>
  <pre><code>[root@test3 k8s]# kubectl -n kube-system get service
  NAME                        TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)                     AGE
  kube-dns                    ClusterIP   10.96.0.10      &lt;none&gt;        53/UDP,53/TCP,9153/TCP      75d
  </code></pre>
  <p><code>core dns</code></p>
  <pre><code>[root@test3 k8s]# kubectl -n kube-system get  pod -o wide | grep core
  coredns-6557d7f7d6-5nkv7                             1/1     Running   0          10d   10.244.0.14    test3.weikayuninternal.com   &lt;none&gt;           &lt;none&gt;
  coredns-6557d7f7d6-gtrgc                             1/1     Running   0          10d   10.244.0.13    test3.weikayuninternal.com   &lt;none&gt;           &lt;none&gt;
  </code></pre>
  <p>when I change the nameserver ip to coredns ip.  resolve dns is ok.</p>
  <pre><code>/ # cat /etc/resolv.conf 
  nameserver 10.244.0.14
  #nameserver 10.96.0.10
  search weika.svc.cluster.local svc.cluster.local cluster.local
  options ndots:5
  / # ping stackoverflow.com
  PING stackoverflow.com (151.101.65.69): 56 data bytes
  64 bytes from 151.101.65.69: seq=0 ttl=49 time=100.497 ms
  64 bytes from 151.101.65.69: seq=1 ttl=49 time=101.014 ms
  64 bytes from 151.101.65.69: seq=2 ttl=49 time=100.462 ms
  64 bytes from 151.101.65.69: seq=3 ttl=49 time=101.465 ms
  64 bytes from 151.101.65.69: seq=4 ttl=49 time=100.318 ms
  ^C
  --- stackoverflow.com ping statistics ---
  5 packets transmitted, 5 packets received, 0% packet loss
  round-trip min/avg/max = 100.318/100.751/101.465 ms
  / # 
  </code></pre>
  <p>Why is it happening?</p>