diff --git a/ospf6d/ospf6_message.h b/ospf6d/ospf6_message.h
index ebb6308..b24d2e6 100644
--- a/ospf6d/ospf6_message.h
+++ b/ospf6d/ospf6_message.h
@@ -52,6 +52,7 @@
   (ospf6_message_type_str[ OSPF6_MESSAGE_TYPE_CANONICAL (T) ])
 
 /* OSPFv3 packet header */
+#define OSPF6_HEADER_SIZE                     16U
 struct ospf6_header
 {
   u_char    version;
@@ -67,6 +68,7 @@
 #define OSPF6_MESSAGE_END(H) ((caddr_t) (H) + ntohs ((H)->length))
 
 /* Hello */
+#define OSPF6_HELLO_MIN_SIZE                  20U
 struct ospf6_hello
 {
   u_int32_t interface_id;
@@ -80,6 +82,7 @@
 };
 
 /* Database Description */
+#define OSPF6_DB_DESC_MIN_SIZE                12U
 struct ospf6_dbdesc
 {
   u_char    reserved1;
@@ -96,7 +99,9 @@
 #define OSPF6_DBDESC_IBIT  (0x04) /* initial bit */
 
 /* Link State Request */
+#define OSPF6_LS_REQ_MIN_SIZE                  0U
 /* It is just a sequence of entries below */
+#define OSPF6_LSREQ_LSDESC_FIX_SIZE           12U
 struct ospf6_lsreq_entry
 {
   u_int16_t reserved;     /* Must Be Zero */
@@ -106,6 +111,7 @@
 };
 
 /* Link State Update */
+#define OSPF6_LS_UPD_MIN_SIZE                  4U
 struct ospf6_lsupdate
 {
   u_int32_t lsa_number;
@@ -113,6 +119,7 @@
 };
 
 /* Link State Acknowledgement */
+#define OSPF6_LS_ACK_MIN_SIZE                  0U
 /* It is just a sequence of LSA Headers */
 
 /* Function definition */