diff --git a/tools/init-runonce b/tools/init-runonce
index 883f5dfeed..868863717b 100755
--- a/tools/init-runonce
+++ b/tools/init-runonce
@@ -9,6 +9,8 @@ IMAGE_URL=http://download.cirros-cloud.net/0.3.5/
 IMAGE=cirros-0.3.5-x86_64-disk.img
 IMAGE_NAME=cirros
 IMAGE_TYPE=linux
+
+# This EXT_NET_CIDR is your public network,that you want to connect to the internet via.
 EXT_NET_CIDR='10.0.2.0/24'
 EXT_NET_RANGE='start=10.0.2.150,end=10.0.2.199'
 EXT_NET_GATEWAY='10.0.2.1'