Update weave-network-policy.md (#4683)

* Update weave-network-policy.md

add weavenet networkpolicy example

* Edits from zacharysarah

* Merge branch 'master' into patch-10

* Merge branch 'patch-10' of github.com:dengyi1996/kubernetes.github.io into patch-10

* Merge branch 'master' into patch-10

docs/tasks/administer-cluster/weave-network-policy.md

@@ -26,9 +26,89 @@ The Weave Net Addon for Kubernetes comes with a [Network Policy Controller](http
 
 {% endcapture %}
 
+{% capture example %}
+
+## Namespace isolation example
+
+1. Create a namespace with `DefaultDeny`.
+
+```yaml
+kind: Namespace
+apiVersion: v1
+metadata:
+  name: myns
+  annotations:
+    net.beta.kubernetes.io/network-policy: |
+      {
+        "ingress": {
+          "isolation": "DefaultDeny"
+        }
+      }
+```
+
+2. Create 2 pods inside this namespace.
+
+```yaml
+kind: Pod
+apiVersion: v1
+metadata:
+  name: pod1
+  namespace: myns
+  labels:
+    inns: "yes"
+spec:
+  containers:
+  - name: pod1
+    image: nginx
+---
+kind: Pod
+apiVersion: v1
+metadata:
+  name: pod2
+  namespace: myns
+  labels:
+    inns: "yes"
+spec:
+  containers:
+  - name: pod2
+    image: nginx
+```
+
+3. Get the IP addresses of the pods.
+
+```shell
+kubectl get po -n myns -o wide
+```
+**Note:** If your cURL requests to pods are forbidden, try making cURL requests to other pods from within a pod.
+{: .note}
+
+4. Create a Kubernetes NetworkPolicy that allows pods within the same namespace to connect with each other.
+
+```yaml
+apiVersion: networking.k8s.io/v1
+kind: NetworkPolicy
+metadata:
+  name: aaa
+  namespace: myns
+spec:
+  podSelector:
+    matchExpressions:
+      - {key: inns, operator: In, values: ["yes"]}
+  ingress:
+    - from:
+        - podSelector:
+             matchExpressions:
+               - {key: inns, operator: In, values: ["yes"]}
+```
+**Caution:** After applying the network policy, pods outside the namespace you specify may be unable to connect with pods inside the namespace.
+{. :caution}
+
+{% endcapture %}
+
+
 {% capture whatsnext %}
 
-Once you have installed the Weave Net Addon you can follow the [NetworkPolicy getting started guide](/docs/getting-started-guides/network-policy/walkthrough) to try out Kubernetes NetworkPolicy.
+Once you have installed the Weave Net addon, you can follow the [NetworkPolicy getting started guide](/docs/getting-started-guides/network-policy/walkthrough) to try out Kubernetes NetworkPolicy.
 
 {% endcapture %}