+#define IPPROTO_TCP 6
+#define TCP_HDRLEN 20
+#define TH_FIN 0x01
+
+/*
+ * We use these macros because the IP header may be at an odd address,
+ * and some compilers might use word loads to get th_off or ip_hl.
+ */
+
+#define net_short(x) (((x)[0] << 8) + (x)[1])
+#define get_iphl(x) (((unsigned char *)(x))[0] & 0xF)
+#define get_ipoff(x) net_short((unsigned char *)(x) + 6)
+#define get_ipproto(x) (((unsigned char *)(x))[9])
+#define get_tcpoff(x) (((unsigned char *)(x))[12] >> 4)
+#define get_tcpflags(x) (((unsigned char *)(x))[13])