--- res/res_pjsip_sdp_rtp.c	(Asterisk 13.10.0)
+++ res/res_pjsip_sdp_rtp.c	(working copy)
@@ -1057,6 +1057,20 @@
 		/* If no type formats are configured don't add a stream */
 		return 0;
-	} else if (!session_media->rtp && create_rtp(session, session_media, session->endpoint->media.rtp.ipv6)) {
-		return -1;
+	} else if (!session_media->rtp) {
+		unsigned int ip6;
+
+		if (session->contact) {
+			/* IP6 addresses contain at least one colon. IP4 do not, because
+			 * a port is stored in another variable: contact->via_port
+			 */
+			ip6 = strstr(session->contact->via_addr, ":") ? 1 : 0;
+		} else {
+			ast_log(LOG_ERROR, "Cannot determine whether to use IP4 or IP6; falling back to rtp_ipv6 of endpoint. Please, report as issue!\n");
+			ip6 = session->endpoint->media.rtp.ipv6;
+		}
+
+		if (create_rtp(session, session_media, ip6)) {
+			return -1;
+		}
 	}
 
@@ -1084,8 +1098,9 @@
 
 	/* Add connection level details */
+	ast_rtp_instance_get_local_address(session_media->rtp, &addr);
 	if (direct_media_enabled) {
 		hostip = ast_sockaddr_stringify_fmt(&session_media->direct_media_addr, AST_SOCKADDR_STR_ADDR);
 	} else if (ast_strlen_zero(session->endpoint->media.address)) {
-		hostip = ast_sip_get_host_ip_string(session->endpoint->media.rtp.ipv6 ? pj_AF_INET6() : pj_AF_INET());
+		hostip = ast_sip_get_host_ip_string((ast_sockaddr_is_ipv6(&addr)) ? pj_AF_INET6() : pj_AF_INET());
 	} else {
 		hostip = session->endpoint->media.address;
@@ -1098,7 +1113,6 @@
 
 	media->conn->net_type = STR_IN;
-	media->conn->addr_type = session->endpoint->media.rtp.ipv6 ? STR_IP6 : STR_IP4;
+	media->conn->addr_type = (ast_sockaddr_is_ipv6(&addr)) ? STR_IP6 : STR_IP4;
 	pj_strdup2(pool, &media->conn->addr, hostip);
-	ast_rtp_instance_get_local_address(session_media->rtp, &addr);
 	media->desc.port = direct_media_enabled ? ast_sockaddr_port(&session_media->direct_media_addr) : (pj_uint16_t) ast_sockaddr_port(&addr);
 	media->desc.port_count = 1;
@@ -1235,6 +1249,22 @@
 
 	/* Create an RTP instance if need be */
-	if (!session_media->rtp && create_rtp(session, session_media, session->endpoint->media.rtp.ipv6)) {
-		return -1;
+	if (!session_media->rtp) {
+		unsigned int ip6;
+
+		if (remote_stream->conn) { /* query RTP, but c= is optional */
+			ip6 = pj_stricmp2(&remote_stream->conn->addr_type, "IP4");
+		} else if (session->contact) { /* query SIP */
+			/* IP6 addresses contain at least one colon. IP4 do not, because
+			 * a port is stored in another variable: contact->via_port
+			 */
+			ip6 = strstr(session->contact->via_addr, ":") ? 1 : 0;
+		} else {
+			ast_log(LOG_ERROR, "Cannot determine whether to use IP4 or IP6; falling back to rtp_ipv6 of endpoint. Please, report as issue!\n");
+			ip6 = session->endpoint->media.rtp.ipv6;
+		}
+
+		if (create_rtp(session, session_media, ip6)) {
+			return -1;
+		}
 	}
 
--- res/res_pjsip_session.c	(Asterisk 13.10.0)
+++ res/res_pjsip_session.c	(working copy)
@@ -2844,11 +2844,23 @@
 		}
 	} else {
+		unsigned int ip6;
+
+		if (session->contact) {
+			/* IP6 addresses contain at least one colon. IP4 do not, because
+			 * a port is stored in another variable: contact->via_port
+			 */
+			ip6 = strstr(session->contact->via_addr, ":") ? 1 : 0;
+		} else {
+			ast_log(LOG_ERROR, "Cannot determine whether to use IP4 or IP6; falling back to rtp_ipv6 of endpoint. Please, report as issue!\n");
+			ip6 = session->endpoint->media.rtp.ipv6;
+		}
+
 		local->origin.net_type = STR_IN;
-		local->origin.addr_type = session->endpoint->media.rtp.ipv6 ? STR_IP6 : STR_IP4;
+		local->origin.addr_type = ip6 ? STR_IP6 : STR_IP4;
 
 		if (!ast_strlen_zero(session->endpoint->media.address)) {
 			pj_strdup2(inv->pool_prov, &local->origin.addr, session->endpoint->media.address);
 		} else {
-			pj_strdup2(inv->pool_prov, &local->origin.addr, ast_sip_get_host_ip_string(session->endpoint->media.rtp.ipv6 ? pj_AF_INET6() : pj_AF_INET()));
+			pj_strdup2(inv->pool_prov, &local->origin.addr, ast_sip_get_host_ip_string(ip6 ? pj_AF_INET6() : pj_AF_INET()));
 		}
 	}
--- res/res_pjsip_t38.c	(Asterisk 13.10.0)
+++ res/res_pjsip_t38.c	(working copy)
@@ -256,10 +256,22 @@
 static int t38_initialize_session(struct ast_sip_session *session, struct ast_sip_session_media *session_media)
 {
+	unsigned int ip6;
+
 	if (session_media->udptl) {
 		return 0;
 	}
 
+	if (session->contact) {
+		/* IP6 addresses contain at least one colon. IP4 do not, because
+		 * a port is stored in another variable: contact->via_port
+		 */
+		ip6 = strstr(session->contact->via_addr, ":") ? 1 : 0;
+	} else {
+		ast_log(LOG_ERROR, "Cannot determine whether to use IP4 or IP6; falling back to t38_udptl_ipv6 of endpoint. Please, report as issue!\n");
+		ip6 = session->endpoint->media.t38.ipv6;
+	}
+
 	if (!(session_media->udptl = ast_udptl_new_with_bindaddr(NULL, NULL, 0,
-		session->endpoint->media.t38.ipv6 ? &address_ipv6 : &address_ipv4))) {
+		ip6 ? &address_ipv6 : &address_ipv4))) {
 		return -1;
 	}
@@ -699,12 +711,4 @@
 	}
 
-	/* Check the address family to make sure it matches configured */
-	if ((ast_sockaddr_is_ipv6(addrs) && !session->endpoint->media.t38.ipv6) ||
-		(ast_sockaddr_is_ipv4(addrs) && session->endpoint->media.t38.ipv6)) {
-		/* The address does not match configured */
-		ast_debug(3, "Declining, provided host does not match configured address family\n");
-		return -1;
-	}
-
 	return 1;
 }
@@ -730,4 +734,5 @@
 	char tmp[512];
 	pj_str_t stmp;
+	unsigned int ip6;
 
 	if (!session->endpoint->media.t38.enabled) {
@@ -753,6 +758,16 @@
 	media->desc.transport = STR_UDPTL;
 
+	if (session->contact) {
+		/* IP6 addresses contain at least one colon. IP4 do not, because
+		 * a port is stored in another variable: contact->via_port
+		 */
+		ip6 = strstr(session->contact->via_addr, ":") ? 1 : 0;
+	} else {
+		ast_log(LOG_ERROR, "Cannot determine whether to use IP4 or IP6; falling back to t38_udptl_ipv6 of endpoint. Please, report as issue!\n");
+		ip6 = session->endpoint->media.t38.ipv6;
+	}
+
 	if (ast_strlen_zero(session->endpoint->media.address)) {
-		hostip = ast_sip_get_host_ip_string(session->endpoint->media.t38.ipv6 ? pj_AF_INET6() : pj_AF_INET());
+		hostip = ast_sip_get_host_ip_string(ip6 ? pj_AF_INET6() : pj_AF_INET());
 	} else {
 		hostip = session->endpoint->media.address;
@@ -765,5 +780,5 @@
 
 	media->conn->net_type = STR_IN;
-	media->conn->addr_type = session->endpoint->media.t38.ipv6 ? STR_IP6 : STR_IP4;
+	media->conn->addr_type = ip6 ? STR_IP6 : STR_IP4;
 	pj_strdup2(pool, &media->conn->addr, hostip);
 	ast_udptl_get_us(session_media->udptl, &addr);
--- contrib/scripts/sip_to_pjsip/sip_to_pjsip.py	(Asterisk 13.10.0)
+++ contrib/scripts/sip_to_pjsip/sip_to_pjsip.py	(working copy)
@@ -371,2 +371 @@
-# type, rtp_ipv6, 100rel, trust_id_outbound, aggregate_mwi,
-# connected_line_method
+# type, 100rel, trust_id_outbound, aggregate_mwi, connected_line_method
--- configs/samples/pjsip.conf.sample	(Asterisk 13.10.0)
+++ configs/samples/pjsip.conf.sample	(working copy)
@@ -115,3 +114,0 @@
-; IPv6: For endpoints using IPv6, remember to set "rtp_ipv6=yes" so that the RTP
-; engine will also be able to bind to an IPv6 address.
-;
@@ -297,2 +293,0 @@
-; Use the "rtp_ipv6=yes" option if you want to utilize RTP over an ipv6 transport.
-;
@@ -317,2 +311,0 @@
-;transport=transport-udp-ipv6
-;rtp_ipv6=yes
@@ -647 +639,0 @@
-;rtp_ipv6=no    ; Allow use of IPv6 for RTP traffic (default: "no")
@@ -696,2 +687,0 @@
-;t38_udptl_ipv6=no      ; Whether IPv6 is used for UDPTL Sessions (default:
-                        ; "no")