--- a/cloudinit/net/cmdline.py
+++ b/cloudinit/net/cmdline.py
@@ -86,7 +86,7 @@
         else:
             proto = 'static'
 
-    if proto not in ('static', 'dhcp'):
+    if proto not in ('static', 'dhcp', 'dhcp6'):
         raise ValueError("Unexpected value for PROTO: %s" % proto)
 
     iface = {
@@ -98,12 +98,15 @@
     if name in mac_addrs:
         iface['mac_address'] = mac_addrs[name]
 
-    # originally believed there might be IPV6* values
-    for v, pre in (('ipv4', 'IPV4'),):
+    # Handle both IPv4 and IPv6 values
+    for v, pre in (('ipv4', 'IPV4'), ('ipv6', 'IPV6')):
         # if no IPV4ADDR or IPV6ADDR, then go on.
         if pre + "ADDR" not in data:
             continue
-        subnet = {'type': proto, 'control': 'manual'}
+        if pre + "PROTO" in data:
+            subnet = {'type': data[pre + 'PROTO'], 'control': 'manual'}
+        else:
+            subnet = {'type': proto, 'control': 'manual'}
 
         # these fields go right on the subnet
         for key in ('NETMASK', 'BROADCAST', 'GATEWAY'):