--- openflow-2010-09-24-5.h	2015-07-23 09:54:16.056479317 -0700
+++ openflow-2010-09-24-6.h	2015-07-23 09:54:16.060479318 -0700
@@ -611,6 +611,8 @@
 };
 OFP_ASSERT(sizeof(struct ofp_group_mod) == 16);
 
+/* Group types.  Values in the range [128, 255] are reserved for experimental
+ * use. */
 enum ofp_group_type {
     OFPGT_FLOOD,    /* Flood group.  */
     OFPGT_MPATH,    /* Multipath group. */