diff --git a/home/rdns.go b/home/rdns.go
index c8a39974..abdea47f 100644
--- a/home/rdns.go
+++ b/home/rdns.go
@@ -1,12 +1,13 @@
 package home
 
 import (
+	"encoding/binary"
 	"fmt"
 	"strings"
-	"sync"
 	"time"
 
 	"github.com/AdguardTeam/dnsproxy/upstream"
+	"github.com/AdguardTeam/golibs/cache"
 	"github.com/AdguardTeam/golibs/log"
 	"github.com/miekg/dns"
 )
@@ -18,12 +19,14 @@ const (
 // RDNS - module context
 type RDNS struct {
 	clients   *clientsContainer
-	ipChannel chan string // pass data from DNS request handling thread to rDNS thread
-	// contains IP addresses of clients to be resolved by rDNS
-	// if IP address couldn't be resolved, it stays here forever to prevent further attempts to resolve the same IP
-	ips      map[string]bool
-	lock     sync.Mutex        // synchronize access to 'ips'
-	upstream upstream.Upstream // Upstream object for our own DNS server
+	ipChannel chan string       // pass data from DNS request handling thread to rDNS thread
+	upstream  upstream.Upstream // Upstream object for our own DNS server
+
+	// Contains IP addresses of clients to be resolved by rDNS
+	// If IP address is resolved, it stays here while it's inside Clients.
+	//  If it's removed from Clients, this IP address will be resolved once again.
+	// If IP address couldn't be resolved, it stays here for some time to prevent further attempts to resolve the same IP.
+	ipAddrs cache.Cache
 }
 
 // InitRDNS - create module context
@@ -47,7 +50,11 @@ func InitRDNS(clients *clientsContainer) *RDNS {
 		return nil
 	}
 
-	r.ips = make(map[string]bool)
+	cconf := cache.Config{}
+	cconf.EnableLRU = true
+	cconf.MaxCount = 10000
+	r.ipAddrs = cache.New(cconf)
+
 	r.ipChannel = make(chan string, 256)
 	go r.workerLoop()
 	return &r
@@ -55,25 +62,30 @@ func InitRDNS(clients *clientsContainer) *RDNS {
 
 // Begin - add IP address to rDNS queue
 func (r *RDNS) Begin(ip string) {
+	now := uint64(time.Now().Unix())
+	expire := r.ipAddrs.Get([]byte(ip))
+	if len(expire) != 0 {
+		exp := binary.BigEndian.Uint64(expire)
+		if exp > now {
+			return
+		}
+		// TTL expired
+	}
+	expire = make([]byte, 8)
+	const ttl = 12 * 60 * 60
+	binary.BigEndian.PutUint64(expire, now+ttl)
+	_ = r.ipAddrs.Set([]byte(ip), expire)
+
 	if r.clients.Exists(ip, ClientSourceRDNS) {
 		return
 	}
 
-	// add IP to ips, if not exists
-	r.lock.Lock()
-	defer r.lock.Unlock()
-	_, ok := r.ips[ip]
-	if ok {
-		return
-	}
-	r.ips[ip] = true
-
-	log.Tracef("Adding %s for rDNS resolve", ip)
+	log.Tracef("rDNS: adding %s", ip)
 	select {
 	case r.ipChannel <- ip:
 		//
 	default:
-		log.Tracef("rDNS queue is full")
+		log.Tracef("rDNS: queue is full")
 	}
 }
 
@@ -132,10 +144,6 @@ func (r *RDNS) workerLoop() {
 			continue
 		}
 
-		r.lock.Lock()
-		delete(r.ips, ip)
-		r.lock.Unlock()
-
 		_, _ = config.clients.AddHost(ip, host, ClientSourceRDNS)
 	}
 }
diff --git a/home/whois.go b/home/whois.go
index 1f7eafba..f7c90a2f 100644
--- a/home/whois.go
+++ b/home/whois.go
@@ -1,13 +1,14 @@
 package home
 
 import (
+	"encoding/binary"
 	"fmt"
 	"io/ioutil"
 	"net"
 	"strings"
-	"sync"
 	"time"
 
+	"github.com/AdguardTeam/golibs/cache"
 	"github.com/AdguardTeam/golibs/log"
 )
 
@@ -20,10 +21,13 @@ const (
 // Whois - module context
 type Whois struct {
 	clients     *clientsContainer
-	ips         map[string]bool
-	lock        sync.Mutex
 	ipChan      chan string
 	timeoutMsec uint
+
+	// Contains IP addresses of clients
+	// An active IP address is resolved once again after it expires.
+	// If IP address couldn't be resolved, it stays here for some time to prevent further attempts to resolve the same IP.
+	ipAddrs cache.Cache
 }
 
 // Create module context
@@ -31,7 +35,12 @@ func initWhois(clients *clientsContainer) *Whois {
 	w := Whois{}
 	w.timeoutMsec = 5000
 	w.clients = clients
-	w.ips = make(map[string]bool)
+
+	cconf := cache.Config{}
+	cconf.EnableLRU = true
+	cconf.MaxCount = 10000
+	w.ipAddrs = cache.New(cconf)
+
 	w.ipChan = make(chan string, 255)
 	go w.workerLoop()
 	return &w
@@ -186,14 +195,19 @@ func (w *Whois) process(ip string) [][]string {
 
 // Begin - begin requesting WHOIS info
 func (w *Whois) Begin(ip string) {
-	w.lock.Lock()
-	_, found := w.ips[ip]
-	if found {
-		w.lock.Unlock()
-		return
+	now := uint64(time.Now().Unix())
+	expire := w.ipAddrs.Get([]byte(ip))
+	if len(expire) != 0 {
+		exp := binary.BigEndian.Uint64(expire)
+		if exp > now {
+			return
+		}
+		// TTL expired
 	}
-	w.ips[ip] = true
-	w.lock.Unlock()
+	expire = make([]byte, 8)
+	const ttl = 12 * 60 * 60
+	binary.BigEndian.PutUint64(expire, now+ttl)
+	_ = w.ipAddrs.Set([]byte(ip), expire)
 
 	log.Debug("Whois: adding %s", ip)
 	select {