diff --git a/dns_client.c b/dns_client.c
index acf3a3d..6d706c8 100644
--- a/dns_client.c
+++ b/dns_client.c
@@ -174,9 +174,9 @@ int _dns_client_server_add(char *server_ip, struct addrinfo *gai, dns_server_typ
 	}
 	memcpy(&server_info->addr, gai->ai_addr, gai->ai_addrlen);
 
-	if (fast_ping_start(server_ip, 0, 60000, NULL, server_info) == NULL) {
-		goto errout;
-	}
+	// if (fast_ping_start(server_ip, 0, 60000, NULL, server_info) == NULL) {
+	// 	goto errout;
+	// }
 
 	pthread_mutex_lock(&client.server_list_lock);
 	list_add(&server_info->list, &client.dns_server_list);
@@ -205,9 +205,9 @@ int _dns_client_server_remove(char *server_ip, struct addrinfo *gai, dns_server_
 		}
 		list_del(&server_info->list);
 		pthread_mutex_unlock(&client.server_list_lock);
-		if (fast_ping_stop(server_info->ping_host) != 0) {
-			tlog(TLOG_ERROR, "stop ping failed.\n");
-		}
+		// if (fast_ping_stop(server_info->ping_host) != 0) {
+		// 	tlog(TLOG_ERROR, "stop ping failed.\n");
+		// }
 		free(server_info);
 		return 0;
 	}
diff --git a/dns_client.h b/dns_client.h
index abb227c..1864e44 100644
--- a/dns_client.h
+++ b/dns_client.h
@@ -10,14 +10,6 @@ typedef enum {
 	DNS_SERVER_TYPE_END,
 } dns_server_type_t;
 
-struct dns_result {
-	char alias[DNS_MAX_CNAME_LEN];
-	unsigned long ttl_v4;
-	unsigned char addr_ipv4[4];
-	unsigned long ttl_v6;
-	unsigned char addr_ipv6[16];
-};
-
 typedef enum dns_result_type {
 	DNS_QUERY_ERR,
 	DNS_QUERY_RESULT = 1,
diff --git a/dns_server.c b/dns_server.c
index c2ca076..1e2232c 100644
--- a/dns_server.c
+++ b/dns_server.c
@@ -58,6 +58,16 @@ struct dns_server {
 	DECLARE_HASHTABLE(hostmap, 6);
 };
 
+struct dns_ip_address {
+	struct hlist_node node;
+	dns_type_t addr_type;
+	union {
+		unsigned char ipv4_addr[DNS_RR_A_LEN];
+		unsigned char ipv6_addr[DNS_RR_AAAA_LEN];
+		unsigned char addr[0];
+	};
+};
+
 struct dns_request {
 	atomic_t refcnt;
 	struct hlist_node map;
@@ -94,6 +104,8 @@ struct dns_request {
 	atomic_t notified;
 
 	int passthrough;
+
+	DECLARE_HASHTABLE(ip_map, 4);
 };
 
 static struct dns_server server;
@@ -255,6 +267,10 @@ int _dns_server_request_complete(struct dns_request *request)
 
 void _dns_server_request_release(struct dns_request *request)
 {
+	struct dns_ip_address *addr_map;
+	struct hlist_node *tmp;
+	int bucket = 0;
+
 	int refcnt = atomic_dec_return(&request->refcnt);
 	if (refcnt) {
 		if (refcnt < 0) {
@@ -265,6 +281,10 @@ void _dns_server_request_release(struct dns_request *request)
 	}
 
 	_dns_server_request_complete(request);
+	hash_for_each_safe(request->ip_map, bucket, tmp, addr_map, node) {
+		hash_del(&addr_map->node);
+		free(addr_map);
+	}
 	memset(request, 0, sizeof(*request));
 	free(request);
 }
@@ -337,6 +357,47 @@ void _dns_server_ping_result(struct ping_host_struct *ping_host, const char *hos
 	}
 }
 
+int _dns_ip_address_check_add(struct dns_request *request, unsigned char *addr, dns_type_t addr_type)
+{
+	int key = 0;
+	struct dns_ip_address *addr_map = NULL;
+	int addr_len = 0;
+
+	if (addr_type == DNS_T_A) {
+		addr_len = DNS_RR_A_LEN;
+	} else if (addr_type == DNS_T_AAAA) {
+		addr_len = DNS_RR_AAAA_LEN;
+	} else {
+		return -1;
+	}
+
+	key = jhash(addr, addr_len, 0);
+	hash_for_each_possible(request->ip_map, addr_map, node, key)
+	{
+		if (addr_type == DNS_T_A) {
+			if (memcmp(addr_map->ipv4_addr, addr, addr_len) == 0) {
+				return -1;
+			}
+		} else if (addr_type == DNS_T_AAAA) {
+			if (memcmp(addr_map->ipv6_addr, addr, addr_len) == 0) {
+				return -1;
+			}
+		}
+	}
+
+	addr_map = malloc(sizeof(*addr_map));
+	if (addr_map == NULL) {
+		tlog(TLOG_ERROR, "malloc failed");
+		return -1;
+	}
+
+	addr_map->addr_type = addr_type;
+	memcpy(addr_map->addr, addr, addr_len);
+	hash_add(request->ip_map, &addr_map->node, key);
+
+	return 0;
+}
+
 static int _dns_client_process_answer(struct dns_request *request, char *domain, struct dns_packet *packet)
 {
 	int ttl;
@@ -363,12 +424,16 @@ static int _dns_client_process_answer(struct dns_request *request, char *domain,
 			switch (rrs->type) {
 			case DNS_T_A: {
 				unsigned char addr[4];
+				_dns_server_request_get(request);
 				dns_get_A(rrs, name, DNS_MAX_CNAME_LEN, &ttl, addr);
+				if (_dns_ip_address_check_add(request, addr, DNS_T_A) != 0) {
+					_dns_server_request_release(request);
+					break;
+				}
 				tlog(TLOG_INFO, "%s %d : %d.%d.%d.%d", name, ttl, addr[0], addr[1], addr[2], addr[3]);
 				sprintf(ip, "%d.%d.%d.%d", addr[0], addr[1], addr[2], addr[3]);
 
 				if (strncmp(name, domain, DNS_MAX_CNAME_LEN) == 0 || strncmp(request->alias, name, DNS_MAX_CNAME_LEN) == 0) {
-					_dns_server_request_get(request);
 					if (fast_ping_start(ip, 1, 1000, _dns_server_ping_result, request) == NULL) {
 						_dns_server_request_release(request);
 					}
@@ -376,10 +441,15 @@ static int _dns_client_process_answer(struct dns_request *request, char *domain,
 			} break;
 			case DNS_T_AAAA: {
 				unsigned char addr[16];
+				_dns_server_request_get(request);
 				dns_get_AAAA(rrs, name, DNS_MAX_CNAME_LEN, &ttl, addr);
+				if (_dns_ip_address_check_add(request, addr, DNS_T_AAAA) != 0) {
+					_dns_server_request_release(request);
+					break;
+				}
+
 				sprintf(name, "%x%x:%x%x:%x%x:%x%x:%x%x:%x%x:%x%x:%x%x", addr[0], addr[1], addr[2], addr[3], addr[4], addr[5], addr[6], addr[7], addr[8],
 						addr[9], addr[10], addr[11], addr[12], addr[13], addr[14], addr[15]);
-				_dns_server_request_get(request);
 				if (fast_ping_start(name, 1, 1000, _dns_server_ping_result, request) == NULL) {
 					_dns_server_request_release(request);
 				}
@@ -547,6 +617,7 @@ static int _dns_server_recv(unsigned char *inpacket, int inpacket_len, struct so
 
 	request->id = packet->head.id;
 	memcpy(&request->head, &packet->head, sizeof(struct dns_head));
+	hash_init(request->ip_map);
 
 	rrs = dns_get_rrs_start(packet, DNS_RRS_QD, &rr_count);
 	if (rr_count > 1) {
diff --git a/fast_ping.c b/fast_ping.c
index 1e39620..1c93ea2 100755
--- a/fast_ping.c
+++ b/fast_ping.c
@@ -298,7 +298,8 @@ static int _fast_ping_sendping_v6(struct ping_host_struct *ping_host)
 
 	len = sendto(ping_host->fd, &ping_host->packet, sizeof(struct fast_ping_packet), 0, (struct sockaddr *)&ping_host->addr, ping_host->addr_len);
 	if (len < 0 || len != sizeof(struct fast_ping_packet)) {
-		tlog(TLOG_ERROR, "sendto %s\n", strerror(errno));
+		char ping_host_name[PING_MAX_HOSTLEN];
+		tlog(TLOG_ERROR, "sendto %s %s\n", gethost_by_addr(ping_host_name, (struct sockaddr *)&ping_host->addr, ping_host->addr_len), strerror(errno));
 		goto errout;
 	}
 
diff --git a/include/atomic.h b/include/atomic.h
index e5dbbea..a5564fe 100755
--- a/include/atomic.h
+++ b/include/atomic.h
@@ -1,4 +1,3 @@
-//Source: http://golubenco.org/atomic-operations.html
 #ifndef _GENERIC_ATOMIC_H
 #define _GENERIC_ATOMIC_H
 
diff --git a/include/cache.h b/include/cache.h
new file mode 100644
index 0000000..e69a0c6
--- /dev/null
+++ b/include/cache.h
@@ -0,0 +1,22 @@
+#ifndef _GENERIC_CACHE_H
+
+#include "list.h"
+#include "hashtable.h"
+
+struct cache_node {
+	struct hlist_node list;
+};
+
+struct cache_head;
+
+struct cache_head *cache_new(int hashsize, void (*item_free)(struct cache_head *head, struct cache_node *node));
+
+int cache_add(struct cache_head *head, struct cache_node *node, void *key, int key_len);
+
+struct cache_node *cache_lookup(struct cache_head *head, void *key, int key_len);
+
+int cache_update(struct cache_head *head, void *key, int key_len);
+
+void cache_free(struct cache_head *head);
+
+#endif // !_GENERIC_CACHE_H
diff --git a/include/findbit.h b/include/findbit.h
index cac0939..0a6feb9 100644
--- a/include/findbit.h
+++ b/include/findbit.h
@@ -1,4 +1,3 @@
-/* SPDX-License-Identifier: GPL-2.0 */
 #ifndef _TOOLS_LINUX_ASM_GENERIC_BITOPS_FIND_H_
 #define _TOOLS_LINUX_ASM_GENERIC_BITOPS_FIND_H_
 
diff --git a/include/gcc_builtin.h b/include/gcc_builtin.h
index 366813b..0d34b2c 100644
--- a/include/gcc_builtin.h
+++ b/include/gcc_builtin.h
@@ -1,4 +1,3 @@
-/* SPDX-License-Identifier: GPL-2.0 */
 #ifndef _TOOLS_LINUX_COMPILER_H_
 #define _TOOLS_LINUX_COMPILER_H_
 
diff --git a/include/hashtable.h b/include/hashtable.h
index 2823192..f21b2c1 100644
--- a/include/hashtable.h
+++ b/include/hashtable.h
@@ -1,4 +1,3 @@
-/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Statically sized hash table implementation
  * (C) 2012  Sasha Levin <levinsasha928@gmail.com>
diff --git a/lib/cache.c b/lib/cache.c
new file mode 100644
index 0000000..a0b0546
--- /dev/null
+++ b/lib/cache.c
@@ -0,0 +1,8 @@
+#include "cache.h"
+#include <pthread.h>
+
+struct cache_head {
+	struct hlist_head hash_head;
+	int hash_size;
+	pthread_rwlock_t *rwlock;
+};