--- openflow-2009-12-15.h	2015-07-23 09:54:15.820479308 -0700
+++ openflow-2009-10-14-2.h	2015-07-23 09:54:15.824479308 -0700
@@ -522,7 +522,8 @@
     uint8_t pad1[1];           /* Align to 64-bits */
     uint16_t dl_type;          /* Ethernet frame type. */
     uint8_t nw_tos;            /* IP ToS (actually DSCP field, 6 bits). */
-    uint8_t nw_proto;          /* IP protocol. */
+    uint8_t nw_proto;          /* IP protocol or lower 8 bits of
+                                * ARP opcode. */
     uint8_t pad2[2];           /* Align to 64-bits */
     uint32_t nw_src;           /* IP source address. */
     uint32_t nw_dst;           /* IP destination address. */