1 files changed, 18 insertions, 0 deletions

diff --git a/sys/netinet/tcp_seq.h b/sys/netinet/tcp_seq.h
index 9d4adc8bf78f..930734758dd3 100644
--- a/sys/netinet/tcp_seq.h
+++ b/sys/netinet/tcp_seq.h
@@ -81,6 +81,24 @@
 #ifdef _KERNEL
 extern tcp_cc	tcp_ccgen;		/* global connection count */
 
+/*
+ * Increment for tcp_iss each second.
+ * This is designed to increment at the standard 250 KB/s,
+ * but with a random component averaging 128 KB.
+ * We also increment tcp_iss by a quarter of this amount
+ * each time we use the value for a new connection.
+ * If defined, the tcp_random18() macro should produce a
+ * number in the range [0-0x3ffff] that is hard to predict.
+ * 
+ * The variable tcp_iss and tcp_random18() are only used
+ * by sequence number generation scheme 0.
+ */
+#ifndef tcp_random18
+#define	tcp_random18()	(arc4random() & 0x3ffff)
+#endif
+#define	TCP_ISSINCR	(122*1024 + tcp_random18())
+
+extern tcp_seq	tcp_iss;
 #else
 #define	TCP_ISSINCR	(250*1024)	/* increment for tcp_iss each second */
 #endif /* _KERNEL */