diff --git a/etc/smartdns/smartdns.conf b/etc/smartdns/smartdns.conf
index 9d8d53e..c86d8e4 100644
--- a/etc/smartdns/smartdns.conf
+++ b/etc/smartdns/smartdns.conf
@@ -36,9 +36,14 @@ cache-size 512
 # List of IPs that will be filtered when nameserver is configured -blacklist-ip parameter
 # blacklist-ip [ip/subnet]
 
-# force AAAA query return SO
+# force AAAA query return SOA
 # force-AAAA-SOA [yes|no]
 
+# enabel ipv4 and ipv6 preference
+# dualstack-preference-threshold [num] (100~10000)
+# dualstack-preference [yes|no]
+# dualstack-preference yes
+
 # ttl for all resource record
 # rr-ttl: ttl for all record
 # rr-ttl-min: minimum ttl for resource record
diff --git a/src/dns_conf.c b/src/dns_conf.c
index 9e82d47..28d7c40 100644
--- a/src/dns_conf.c
+++ b/src/dns_conf.c
@@ -36,6 +36,9 @@ int dns_conf_audit_num = 2;
 art_tree dns_conf_domain_rule;
 radix_tree_t *dns_conf_address_rule;
 
+int dns_conf_dualstack_preference;
+int dns_conf_dualstack_threshold = 1000; // cent usecond
+
 int dns_conf_rr_ttl;
 int dns_conf_rr_ttl_min;
 int dns_conf_rr_ttl_max;
@@ -514,6 +517,8 @@ struct config_item config_item[] = {
 	CONF_INT("tcp-idle-time", &dns_conf_tcp_idle_time, 0, 3600),
 	CONF_INT("cache-size", &dns_conf_cachesize, 0, CONF_INT_MAX),
 	CONF_YESNO("prefetch-domain", &dns_conf_prefetch),
+	CONF_YESNO("dualstack-preference", &dns_conf_dualstack_preference),
+	CONF_INT("dualstack-preference-threshold", &dns_conf_dualstack_threshold, 100, 10000),
 	CONF_CUSTOM("log-level", config_log_level, NULL),
 	CONF_STRING("log-file", (char *)dns_conf_log_file, DNS_MAX_PATH),
 	CONF_SIZE("log-size", &dns_conf_log_size, 0, 1024 * 1024 * 1024),
diff --git a/src/dns_conf.h b/src/dns_conf.h
index f949e06..a8fc1bd 100644
--- a/src/dns_conf.h
+++ b/src/dns_conf.h
@@ -99,6 +99,9 @@ extern char dns_conf_server_name[DNS_MAX_CONF_CNAME_LEN];
 extern art_tree dns_conf_domain_rule;
 extern radix_tree_t *dns_conf_address_rule;
 
+extern int dns_conf_dualstack_preference;
+extern int dns_conf_dualstack_threshold;
+
 extern int dns_conf_rr_ttl;
 extern int dns_conf_rr_ttl_min;
 extern int dns_conf_rr_ttl_max;
diff --git a/src/dns_server.c b/src/dns_server.c
index b2e5742..f4356f4 100644
--- a/src/dns_server.c
+++ b/src/dns_server.c
@@ -148,7 +148,7 @@ struct dns_request {
 
 	/* send original raw packet to server/client like proxy */
 	int passthrough;
-
+	int request_wait;
 	int prefetch;
 
 	pthread_mutex_t ip_map_lock;
@@ -419,6 +419,30 @@ static int _dns_reply(struct dns_request *request)
 	return _dns_reply_inpacket(request, inpacket, encode_len);
 }
 
+static int _dns_server_reply_SOA(int rcode, struct dns_request *request, struct dns_packet *packet)
+{
+	struct dns_soa *soa;
+
+	request->rcode = rcode;
+	request->has_soa = 1;
+	request->has_ipv4 = 0;
+	request->has_ipv6 = 0;
+	request->has_ptr = 0;
+
+	soa = &request->soa;
+
+	strcpy(soa->mname, "a.gtld-servers.net");
+	strcpy(soa->rname, "nstld.verisign-grs.com");
+	soa->serial = 1800;
+	soa->refresh = 1800;
+	soa->retry = 900;
+	soa->expire = 604800;
+	soa->minimum = 86400;
+	_dns_reply(request);
+
+	return 0;
+}
+
 static int _dns_setup_ipset(struct dns_request *request)
 {
 	struct dns_ipset_rule *ipset_rule = NULL;
@@ -489,6 +513,15 @@ int _dns_server_request_complete(struct dns_request *request)
 			 request->ipv6_addr[6], request->ipv6_addr[7], request->ipv6_addr[8], request->ipv6_addr[9], request->ipv6_addr[10], request->ipv6_addr[11],
 			 request->ipv6_addr[12], request->ipv6_addr[13], request->ipv6_addr[14], request->ipv6_addr[15]);
 
+		if (request->has_ipv4) {
+			dns_cache_insert(request->domain, cname, cname_ttl, request->ttl_v4, DNS_T_AAAA, request->ipv4_addr, DNS_RR_A_LEN);
+
+			if ((request->ping_ttl_v4 - dns_conf_dualstack_threshold < request->ping_ttl_v6 ) && (request->ping_ttl_v4 > 0)) {
+				tlog(TLOG_DEBUG, "Force IPV4 perfered.");
+				return _dns_server_reply_SOA(DNS_RC_NOERROR, request, NULL);
+			}
+		}
+
 		if (request->has_ipv6) {
 			if (request->has_ping_result == 0 && request->ttl_v6 > DNS_SERVER_TMOUT_TTL) {
 				request->ttl_v6 = DNS_SERVER_TMOUT_TTL;
@@ -566,6 +599,7 @@ void _dns_server_ping_result(struct ping_host_struct *ping_host, const char *hos
 {
 	struct dns_request *request = userptr;
 	int may_complete = 0;
+	int threshold = 100;
 
 	if (request == NULL) {
 		return;
@@ -579,6 +613,7 @@ void _dns_server_ping_result(struct ping_host_struct *ping_host, const char *hos
 
 	unsigned int rtt = tv->tv_sec * 10000 + tv->tv_usec / 100;
 
+
 	switch (addr->sa_family) {
 	case AF_INET: {
 		struct sockaddr_in *addr_in;
@@ -588,6 +623,10 @@ void _dns_server_ping_result(struct ping_host_struct *ping_host, const char *hos
 			request->has_ipv4 = 1;
 			memcpy(request->ipv4_addr, &addr_in->sin_addr.s_addr, 4);
 		}
+
+		if (dns_conf_dualstack_preference == 1 && request->qtype == DNS_T_AAAA) {
+			threshold = dns_conf_dualstack_threshold;
+		}
 	} break;
 	case AF_INET6: {
 		struct sockaddr_in6 *addr_in6;
@@ -616,7 +655,7 @@ void _dns_server_ping_result(struct ping_host_struct *ping_host, const char *hos
 		tlog(TLOG_DEBUG, "from %15s: seq=%d timeout\n", host, seqno);
 	}
 
-	if (rtt < 100) {
+	if (rtt < threshold) {
 		may_complete = 1;
 	} else if (rtt < (get_tick_count() - request->send_tick) * 10) {
 		may_complete = 1;
@@ -763,7 +802,9 @@ static int _dns_server_process_answer(struct dns_request *request, char *domain,
 				unsigned char addr[4];
 				if (request->qtype != DNS_T_A) {
 					/* ignore non-matched query type */
-					break;
+					if (dns_conf_dualstack_preference == 0) {
+						break;
+					}
 				}
 				_dns_server_request_get(request);
 				dns_get_A(rrs, name, DNS_MAX_CNAME_LEN, &ttl, addr);
@@ -905,6 +946,7 @@ static int dns_server_resolve_callback(char *domain, dns_result_type rtype, unsi
 {
 	struct dns_request *request = user_ptr;
 	int ip_num = 0;
+	int request_wait = 0;
 
 	if (request == NULL) {
 		return -1;
@@ -925,10 +967,12 @@ static int dns_server_resolve_callback(char *domain, dns_result_type rtype, unsi
 	} else {
 		pthread_mutex_lock(&request->ip_map_lock);
 		ip_num = request->ip_map_num;
+		request_wait = request->request_wait;
+		request->request_wait--;
 		pthread_mutex_unlock(&request->ip_map_lock);
 
 		/* Not need to wait check result if only has one ip address */
-		if (ip_num == 1) {
+		if (ip_num == 1 && request_wait == 1) {
 			_dns_server_request_complete(request);
 		}
 
@@ -1014,27 +1058,6 @@ errout:
 	return -1;
 }
 
-static int _dns_server_reply_SOA(int rcode, struct dns_request *request, struct dns_packet *packet)
-{
-	struct dns_soa *soa;
-
-	request->rcode = rcode;
-	request->has_soa = 1;
-
-	soa = &request->soa;
-
-	strcpy(soa->mname, "a.gtld-servers.net");
-	strcpy(soa->rname, "nstld.verisign-grs.com");
-	soa->serial = 1800;
-	soa->refresh = 1800;
-	soa->retry = 900;
-	soa->expire = 604800;
-	soa->minimum = 86400;
-	_dns_reply(request);
-
-	return 0;
-}
-
 static void _dns_server_log_rule(char *domain, unsigned char *rule_key, int rule_key_len)
 {
 	char rule_name[DNS_MAX_CNAME_LEN];
@@ -1278,7 +1301,14 @@ static int _dns_server_recv(struct dns_server_conn *client, unsigned char *inpac
 
 	_dns_server_request_get(request);
 	request->send_tick = get_tick_count();
+
 	dns_client_query(request->domain, qtype, dns_server_resolve_callback, request);
+	request->request_wait++;
+	if (qtype == DNS_T_AAAA && dns_conf_dualstack_preference) {
+		_dns_server_request_get(request);
+		dns_client_query(request->domain, DNS_T_A, dns_server_resolve_callback, request);
+		request->request_wait++;
+	}
 
 	return 0;
 clean_exit:
diff --git a/src/smartdns.c b/src/smartdns.c
index 7fcdbb3..cdaf66d 100644
--- a/src/smartdns.c
+++ b/src/smartdns.c
@@ -285,7 +285,7 @@ void sig_error_exit(int signo, siginfo_t *siginfo, void *context)
 	_exit(0);
 }
 
-int sig_list[] = {SIGSEGV, SIGABRT, SIGPIPE, SIGBUS, SIGILL, SIGFPE};
+int sig_list[] = {SIGSEGV, SIGABRT, SIGBUS, SIGILL, SIGFPE};
 
 int sig_num = sizeof(sig_list) / sizeof(int);
 
@@ -362,11 +362,12 @@ int main(int argc, char *argv[])
 	}
 
 	signal(SIGINT, sig_exit);
+	signal(SIGPIPE, SIG_IGN);
 	atexit(smartdns_exit);
 
 	return smartdns_run();
-
+	
 errout:
 
 	return 1;
-}
\ No newline at end of file
+}