<p>I'm seeing a weird issue on kubernetes and I'm not sure how to debug it.  The k8s environment was installed by kube-up for vsphere using the 2016-01-08 kube.vmdk</p>

<p>The symptom is that the dns for a container in a pod is not working correctly.  When I logon to the kube-dns service to check the settings everything looks correct.  When I ping outside the local network it works as it should but when I ping inside my local network it cannot reach any of the hosts.</p>

<p>For the following my host network is 10.1.1.x, the gateway / dns server is 10.1.1.1.</p>

<h3>inside the kube-dns container:</h3>

<p>(I can ping outside the network by ip and I can ping the gateway just fine.  dns isn't working since the nameserver is unreachable)</p>

<pre><code>kube@kubernetes-master:~$ kubectl --namespace=kube-system exec -ti kube-dns-v20-in2me -- /bin/sh
/ # cat /etc/resolv.conf
nameserver 10.1.1.1
options ndots:5
/ # ping google.com
^C
/ # ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8): 56 data bytes
64 bytes from 8.8.8.8: seq=0 ttl=54 time=13.542 ms
64 bytes from 8.8.8.8: seq=1 ttl=54 time=13.862 ms
^C
--- 8.8.8.8 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 13.542/13.702/13.862 ms
/ # ping 10.1.1.1
PING 10.1.1.1 (10.1.1.1): 56 data bytes
^C
--- 10.1.1.1 ping statistics ---
4 packets transmitted, 0 packets received, 100% packet loss
/ # netstat -r
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
default         10.244.2.1      0.0.0.0         UG        0 0          0 eth0
10.244.2.0      *               255.255.255.0   U         0 0          0 eth0
/ # ping 10.244.2.1
PING 10.244.2.1 (10.244.2.1): 56 data bytes
64 bytes from 10.244.2.1: seq=0 ttl=64 time=0.249 ms
64 bytes from 10.244.2.1: seq=1 ttl=64 time=0.091 ms
^C
--- 10.244.2.1 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.091/0.170/0.249 ms
</code></pre>

<h3>on the master:</h3>

<pre><code>kube@kubernetes-master:~$ netstat -r
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
default         10.1.1.1        0.0.0.0         UG        0 0          0 eth0
10.1.1.0        *               255.255.255.0   U         0 0          0 eth0
10.244.0.0      kubernetes-mini 255.255.255.0   UG        0 0          0 eth0
10.244.1.0      kubernetes-mini 255.255.255.0   UG        0 0          0 eth0
10.244.2.0      kubernetes-mini 255.255.255.0   UG        0 0          0 eth0
10.244.3.0      kubernetes-mini 255.255.255.0   UG        0 0          0 eth0
10.246.0.0      *               255.255.255.0   U         0 0          0 cbr0
172.17.0.0      *               255.255.0.0     U         0 0          0 docker0
kube@kubernetes-master:~$ ping 10.1.1.1
PING 10.1.1.1 (10.1.1.1) 56(84) bytes of data.
64 bytes from 10.1.1.1: icmp_seq=1 ttl=64 time=0.409 ms
64 bytes from 10.1.1.1: icmp_seq=2 ttl=64 time=0.481 ms
^C
--- 10.1.1.1 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 999ms
rtt min/avg/max/mdev = 0.409/0.445/0.481/0.036 ms
</code></pre>

<h3>version:</h3>

<pre><code>kube@kubernetes-master:~$ kubectl version
Client Version: version.Info{Major:"1", Minor:"4", GitVersion:"v1.4.5", GitCommit:"5a0a696437ad35c133c0c8493f7e9d22b0f9b81b", GitTreeState:"clean", BuildDate:"2016-10-29T01:38:40Z", GoVersion:"go1.6.3", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"4", GitVersion:"v1.4.5", GitCommit:"5a0a696437ad35c133c0c8493f7e9d22b0f9b81b", GitTreeState:"clean", BuildDate:"2016-10-29T01:32:42Z", GoVersion:"go1.6.3", Compiler:"gc", Platform:"linux/amd64"}
</code></pre>

<h3>kubernetes-minion-2 (10.244.2.1):</h3>

<p>(Per @der's response adding info from 10.244.2.1)</p>

<pre><code>kube@kubernetes-minion-2:~$ ip addr show cbr0
5: cbr0: &lt;BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP&gt; mtu 1500 qdisc htb state UP group default
    link/ether 8a:ef:b5:fc:28:f4 brd ff:ff:ff:ff:ff:ff
    inet 10.244.2.1/24 scope global cbr0
       valid_lft forever preferred_lft forever
    inet6 fe80::38b5:44ff:fe8a:6d79/64 scope link
       valid_lft forever preferred_lft forever
kube@kubernetes-minion-2:~$ ping google.com
PING google.com (216.58.192.14) 56(84) bytes of data.
64 bytes from nuq04s29-in-f14.1e100.net (216.58.192.14): icmp_seq=1 ttl=52 time=11.8 ms
64 bytes from nuq04s29-in-f14.1e100.net (216.58.192.14): icmp_seq=2 ttl=52 time=11.6 ms
64 bytes from nuq04s29-in-f14.1e100.net (216.58.192.14): icmp_seq=3 ttl=52 time=10.4 ms
^C
--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 10.477/11.343/11.878/0.624 ms
kube@kubernetes-minion-2:~$ ping 10.1.1.1
PING 10.1.1.1 (10.1.1.1) 56(84) bytes of data.
64 bytes from 10.1.1.1: icmp_seq=1 ttl=64 time=0.369 ms
64 bytes from 10.1.1.1: icmp_seq=2 ttl=64 time=0.456 ms
64 bytes from 10.1.1.1: icmp_seq=3 ttl=64 time=0.442 ms
^C
--- 10.1.1.1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 1998ms
rtt min/avg/max/mdev = 0.369/0.422/0.456/0.041 ms
kube@kubernetes-minion-2:~$ netstat -r
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
default         10.1.1.1        0.0.0.0         UG        0 0          0 eth0
10.1.1.0        *               255.255.255.0   U         0 0          0 eth0
10.244.0.0      kubernetes-mini 255.255.255.0   UG        0 0          0 eth0
10.244.1.0      kubernetes-mini 255.255.255.0   UG        0 0          0 eth0
10.244.2.0      *               255.255.255.0   U         0 0          0 cbr0
10.244.3.0      kubernetes-mini 255.255.255.0   UG        0 0          0 eth0
172.17.0.0      *               255.255.0.0     U         0 0          0 docker0
kube@kubernetes-minion-2:~$ routel
         target            gateway          source    proto    scope    dev tbl
        default           10.1.1.1                                     eth0
       10.1.1.0 24                       10.1.1.86   kernel     link   eth0
     10.244.0.0 24       10.1.1.88                                     eth0
     10.244.1.0 24       10.1.1.87                                     eth0
     10.244.2.0 24                      10.244.2.1   kernel     link   cbr0
     10.244.3.0 24       10.1.1.85                                     eth0
     172.17.0.0 16                      172.17.0.1   kernel     linkdocker0
       10.1.1.0          broadcast       10.1.1.86   kernel     link   eth0 local
      10.1.1.86              local       10.1.1.86   kernel     host   eth0 local
     10.1.1.255          broadcast       10.1.1.86   kernel     link   eth0 local
     10.244.2.0          broadcast      10.244.2.1   kernel     link   cbr0 local
     10.244.2.1              local      10.244.2.1   kernel     host   cbr0 local
   10.244.2.255          broadcast      10.244.2.1   kernel     link   cbr0 local
      127.0.0.0          broadcast       127.0.0.1   kernel     link     lo local
      127.0.0.0 8            local       127.0.0.1   kernel     host     lo local
      127.0.0.1              local       127.0.0.1   kernel     host     lo local
127.255.255.255          broadcast       127.0.0.1   kernel     link     lo local
     172.17.0.0          broadcast      172.17.0.1   kernel     linkdocker0 local
     172.17.0.1              local      172.17.0.1   kernel     hostdocker0 local
 172.17.255.255          broadcast      172.17.0.1   kernel     linkdocker0 local
            ::1              local                   kernel              lo
         fe80:: 64                                   kernel            eth0
         fe80:: 64                                   kernel            cbr0
         fe80:: 64                                   kernel         veth6129284
        default        unreachable                   kernel              lo unspec
            ::1              local                     none              lo local
fe80::250:56ff:fe8e:d580              local                     none              lo local
fe80::38b5:44ff:fe8a:6d79              local                     none              lo local
fe80::88ef:b5ff:fefc:28f4              local                     none              lo local
         ff00:: 8                                                      eth0 local
         ff00:: 8                                                      cbr0 local
         ff00:: 8                                                   veth6129284 local
        default        unreachable                   kernel              lo unspec
</code></pre>

<p>How can I diagnose what is going on here?</p>

<p>thanks!</p>

<p>Turns out this is an issue with the default nat routing rules on the minions</p>

<pre><code>$ iptables –t nat –vnxL
...
...
Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes)
    pkts      bytes target     prot opt in     out     source               destination
    ...
    80     4896 MASQUERADE  all  --  *      *       0.0.0.0/0           !10.0.0.0/8           /* kubelet: SNAT outbound cluster traffic */ ADDRTYPE match dst-type !LOCAL
...
...
</code></pre>

<p>This shows that all traffic coming from the 10.x.x.x network gets ignored by the postrouting rules.</p>

<p>If anyone runs across this fix it with:</p>

<pre><code>$ iptables -t nat -I POSTROUTING 1 -s 10.244.0.0/16 -d 10.1.1.1/32 -j MASQUERADE
</code></pre>

<p>where 10.244.x.x/16 is the container network and 10.1.1.1 is the gateway ip</p>
