<p>When I using dig command to test the CoreDNS server,it shows: <code>connection timed out; no servers could be reached</code>:</p>

<pre><code>[root@ops001 ~]# /opt/k8s/bin/kubectl exec -ti soa-user-service-5c8b744d6d-7p9hr -n dabai-fat /bin/sh
/ # dig -t A kubernetes.default.svc.cluster.local. @10.254.0.2

; &lt;&lt;&gt;&gt; DiG 9.12.4-P2 &lt;&lt;&gt;&gt; -t A kubernetes.default.svc.cluster.local. @10.254.0.2
;; global options: +cmd
;; connection timed out; no servers could be reached
</code></pre>

<p>when I ping server,it success.</p>

<pre><code>[root@ops001 ~]# /opt/k8s/bin/kubectl exec -ti soa-user-service-5c8b744d6d-7p9hr -n dabai-fat /bin/sh
/ # ping 10.254.0.2
PING 10.254.0.2 (10.254.0.2): 56 data bytes
64 bytes from 10.254.0.2: seq=0 ttl=64 time=0.100 ms
64 bytes from 10.254.0.2: seq=1 ttl=64 time=0.071 ms
64 bytes from 10.254.0.2: seq=2 ttl=64 time=0.094 ms
64 bytes from 10.254.0.2: seq=3 ttl=64 time=0.087 ms
</code></pre>

<p>why the dig could not connect to DNS server althrough the network is ok?This is my CoreDNS service:</p>

<p><a href="https://i.stack.imgur.com/y5cgy.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/y5cgy.png" alt="enter image description here"></a></p>

<p>when azshara-k8s03‘s node connection to CoreDNS server:</p>

<pre><code>/ # telnet 10.254.0.2 53
Connection closed by foreign host
</code></pre>

<p>when azshara-k8s02‘s and azshara-k8s01‘s node connection to CoreDNS server:</p>

<pre><code>/ # telnet 10.254.0.2 53
telnet: can't connect to remote host (10.254.0.2): Connection refused
</code></pre>

<p>I just confusing why port 53 is not open,when I scan from host using same command,the port 53 is open:</p>

<p><a href="https://i.stack.imgur.com/nqPWy.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nqPWy.png" alt="enter image description here"></a></p>

Dolphin
<p>I finally find some server's kube-proxy not start,and the route foward rule not refresh,using this command to start kube-proxy fix this problem:</p>

<pre><code>systemctl start kube-proxy
</code></pre>
