Apply by doing:
	cd /usr/src
	patch -p0 < 013_isakmpd.patch

And then rebuild and install isakmpd:
        cd sbin/isakmpd
        make obj
        make depend
        make
        make install

Index: sbin/isakmpd/ipsec.c
===================================================================
RCS file: /cvs/src/sbin/isakmpd/ipsec.c,v
retrieving revision 1.121
retrieving revision 1.121.2.1
diff -u -p -r1.121 -r1.121.2.1
--- sbin/isakmpd/ipsec.c	25 Jun 2005 23:20:43 -0000	1.121
+++ sbin/isakmpd/ipsec.c	19 Aug 2006 20:30:22 -0000	1.121.2.1
@@ -2076,9 +2076,10 @@ ipsec_proto_init(struct proto *proto, ch
 {
 	struct ipsec_proto *iproto = proto->data;
 
-	if (proto->sa->phase == 2 && section)
-		iproto->replay_window = conf_get_num(section, "ReplayWindow",
-		    DEFAULT_REPLAY_WINDOW);
+	if (proto->sa->phase == 2)
+		iproto->replay_window = section ? conf_get_num(section,
+		    "ReplayWindow", DEFAULT_REPLAY_WINDOW) :
+		    DEFAULT_REPLAY_WINDOW;
 }
 
 /*