add docs in service concepts

Author: xuzhenglun

content/en/docs/concepts/services-networking/service.md

@@ -586,6 +586,13 @@ spec:
       nodePort: 30007
 ```
 
+#### Reserve Nodeport Ranges to avoid collisions when port assigning 
+
+{{< feature-state for_k8s_version="v1.27" state="alpha" >}}
+
+NodePort's port assignment policy exists for both dynamic auto-assignment and manual assignment by the user. When a user wishes to create a NodePort for a specific port, it may conflict with an already automatically assigned port. To solve this problem, you can turning featuregate `ServiceNodePortStaticSubrange`, which allows you to use a different port allocation strategy for NodePort-type Services, and reducing the risk of collision. The port range for `NodePort` will be divided, and dynamic port assignment will use the upper band by default, once this has been exhausted it will use the lower range. This will allow users to use static allocations on the lower band with a low risk of collision.
+
+
 #### Custom IP address configuration for `type: NodePort` Services {#service-nodeport-custom-listen-address}
 
 You can set up nodes in your cluster to use a particular IP address for serving node port