+#define TCPOPT_SIGNATURE 19 /* Keyed MD5: RFC 2385 */
+#define TCPOLEN_SIGNATURE 18
+
+/* Option definitions */
+#define TCPOPT_SACK_PERMIT_HDR \
+(TCPOPT_NOP<<24|TCPOPT_NOP<<16|TCPOPT_SACK_PERMITTED<<8|TCPOLEN_SACK_PERMITTED)
+#define TCPOPT_SACK_HDR (TCPOPT_NOP<<24|TCPOPT_NOP<<16|TCPOPT_SACK<<8)
+/* Miscellaneous constants */
+#define MAX_SACK_BLKS 6 /* Max # SACK blocks stored at sender side */
+#define TCP_MAX_SACK 3 /* MAX # SACKs sent in any segment */
+