Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 230380)
+++ channels/chan_sip.c	(working copy)
@@ -9055,6 +9055,16 @@
 	}
 }
 
+static void adjust_nat_flags(struct sip_pvt *p)
+{
+	if ((ast_test_flag(&p->flags[0], SIP_NAT) & SIP_NAT_RFC3581)
+		&& ast_test_flag(&p->flags[1], SIP_PAGE2_RPORT_PRESENT)
+		&& !ast_test_flag(&p->flags[0], SIP_NAT_ROUTE)) {
+
+		ast_set_flag(&p->flags[0], SIP_NAT_ROUTE);
+	}
+}
+
 /*! \brief Verify registration of user 
 	- Registration is done in several steps, first a REGISTER without auth
 	  to get a challenge (nonce) then a second one with auth
@@ -9126,6 +9136,8 @@
 			res = AUTH_PEER_NOT_DYNAMIC;
 		} else {
 			ast_copy_flags(&p->flags[0], &peer->flags[0], SIP_NAT);
+			adjust_nat_flags(p);
+
 			transmit_response(p, "100 Trying", req);
 			if (!(res = check_auth(p, req, peer->name, peer->secret, peer->md5secret, SIP_REGISTER, uri, XMIT_UNRELIABLE, ast_test_flag(req, SIP_PKT_IGNORE)))) {
 				if (sip_cancel_destroy(p))
@@ -9887,6 +9899,7 @@
 	if (user && ast_apply_ha(user->ha, sin)) {
 		ast_copy_flags(&p->flags[0], &user->flags[0], SIP_FLAGS_TO_COPY);
 		ast_copy_flags(&p->flags[1], &user->flags[1], SIP_PAGE2_FLAGS_TO_COPY);
+		adjust_nat_flags(p);
 		if (sipmethod == SIP_INVITE) {
 			/* copy channel vars */
 			for (v = user->chanvars ; v ; v = v->next) {
@@ -9920,6 +9933,7 @@
 				ast_log(LOG_WARNING, "Unable to cancel SIP destruction.  Expect bad things.\n");
 			ast_copy_flags(&p->flags[0], &user->flags[0], SIP_FLAGS_TO_COPY);
 			ast_copy_flags(&p->flags[1], &user->flags[1], SIP_PAGE2_FLAGS_TO_COPY);
+			adjust_nat_flags(p);
 			/* Copy SIP extensions profile from INVITE */
 			if (p->sipoptions)
 				user->sipoptions = p->sipoptions;
@@ -10008,6 +10022,7 @@
 			/* Take the peer */
 			ast_copy_flags(&p->flags[0], &peer->flags[0], SIP_FLAGS_TO_COPY);
 			ast_copy_flags(&p->flags[1], &peer->flags[1], SIP_PAGE2_FLAGS_TO_COPY);
+			adjust_nat_flags(p);
 
 			/* Copy SIP extensions profile to peer */
 			if (p->sipoptions)
@@ -10041,6 +10056,7 @@
 			if (!(res = check_auth(p, req, peer->name, p->peersecret, p->peermd5secret, sipmethod, uri2, reliable, ast_test_flag(req, SIP_PKT_IGNORE)))) {
 				ast_copy_flags(&p->flags[0], &peer->flags[0], SIP_FLAGS_TO_COPY);
 				ast_copy_flags(&p->flags[1], &peer->flags[1], SIP_PAGE2_FLAGS_TO_COPY);
+				adjust_nat_flags(p);
 				/* If we have a call limit, set flag */
 				if (peer->call_limit)
 					ast_set_flag(&p->flags[0], SIP_CALL_LIMIT);
@@ -16851,6 +16867,7 @@
 	p->recv = peer->addr;
 	ast_copy_flags(&p->flags[0], &peer->flags[0], SIP_FLAGS_TO_COPY);
 	ast_copy_flags(&p->flags[1], &peer->flags[1], SIP_PAGE2_FLAGS_TO_COPY);
+	adjust_nat_flags(p);
 
 	/* Send OPTIONs to peer's fullcontact */
 	if (!ast_strlen_zero(peer->fullcontact))