Merge pull request #35290 from errordeveloper/new-default-service-cidr

Automatic merge from submit-queue

Change default service IP range to 10.96/12

**What this PR does / why we need it**:

Currently kubeadm defaults to 10.12/12, which turns out to be the same as 10.0/12, which is not exactly obvious until one does CIDR math. The problem with this is that it clashes with some very commonly used ranges like 10.x/8 and 10.x/16.

I find that 10.96/12 would be a reasonable default. We have previously evaluate out-of-the-box configuration in most public clouds and found that 10.x/12 for x > 32 are not used by public cloud providers. Weave Net use 10.32/12, and thereby service IPs should be a range higher then this. Picking 10.96/12 should give user enough visual distinction between pod IPs and services IPs when Weave Net is used.

**Release note**:

```release-note
Change default `kubeadm` service IP range to `10.96.0.0/12`
```

cmd/kubeadm/app/apis/kubeadm/defaults.go

@@ -18,7 +18,7 @@ package kubeadm
 
 const (
 	DefaultServiceDNSDomain  = "cluster.local"
-	DefaultServicesSubnet    = "10.12.0.0/12"
+	DefaultServicesSubnet    = "10.96.0.0/12"
 	DefaultKubernetesVersion = "v1.4.4"
 	DefaultAPIBindPort       = 6443
 	DefaultDiscoveryBindPort = 9898