#define TCPOLEN_SIGNATURE 18
#define TCP_SIGLEN 16 /* length of an option 19 digest */
#define TCPOPT_AUTH 20 /* Enhanced AUTH option */
+#define TCPOPT_UTO 28 /* tcp user timeout (rfc5482) */
+#define TCPOLEN_UTO 4
+
#define TCPOPT_TSTAMP_HDR \
(TCPOPT_NOP<<24|TCPOPT_NOP<<16|TCPOPT_TIMESTAMP<<8|TCPOLEN_TIMESTAMP)