diff --git a/docs/getting-started-guides/centos/centos_manual_config.md b/docs/getting-started-guides/centos/centos_manual_config.md
index 40325c8985..1f1c3ff1dc 100644
--- a/docs/getting-started-guides/centos/centos_manual_config.md
+++ b/docs/getting-started-guides/centos/centos_manual_config.md
@@ -119,6 +119,7 @@ KUBE_API_ARGS=""
 ```
 
 * Configure ETCD to hold the network overlay configuration on master:
+**Warning** This network must be unused in your network infrastructure! `172.40.0.0/16` is free in our network.
 
 ```shell
 $ etcdctl mkdir /kube-centos/network