diff --git a/tools/init-runonce b/tools/init-runonce
index 54708ac1ead540bc4ab6befe8f74875bf13bea2b..4e2de379f76a57e2f90bb789879e07921e2d26c3 100755
--- a/tools/init-runonce
+++ b/tools/init-runonce
@@ -16,9 +16,9 @@ IMAGE_TYPE=linux
 
 # This EXT_NET_CIDR is your public network,that you want to connect to the internet via.
 ENABLE_EXT_NET=${ENABLE_EXT_NET:-1}
-EXT_NET_CIDR='10.0.2.0/24'
-EXT_NET_RANGE='start=10.0.2.150,end=10.0.2.199'
-EXT_NET_GATEWAY='10.0.2.1'
+EXT_NET_CIDR=${EXT_NET_CIDR:-'10.0.2.0/24'}
+EXT_NET_RANGE=${EXT_NET_RANGE:-'start=10.0.2.150,end=10.0.2.199'}
+EXT_NET_GATEWAY=${EXT_NET_GATEWAY:-'10.0.2.1'}
 
 # Sanitize language settings to avoid commands bailing out
 # with "unsupported locale setting" errors.