From 7bfad08ddec0ff2308c7d5f9bd730ed2e586170a Mon Sep 17 00:00:00 2001
From: Ainar Garipov <a.garipov@adguard.com>
Date: Tue, 18 Jul 2023 17:02:07 +0300
Subject: [PATCH] Pull request 1927: 6006-use-address-processor

Updates #6006.

Squashed commit of the following:

commit ac27db95c12858b6ef182a0bd4acebab67a23993
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Jul 18 15:47:17 2023 +0300

    all: imp code

commit 3936288512bfc2d44902ead6ab1bb5711f92b73c
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Jul 17 19:23:46 2023 +0300

    all: imp client resolving
---
 CHANGELOG.md                                  |   3 +
 internal/dnsforward/config.go                 |  12 +-
 internal/dnsforward/dialcontext.go            |  57 ++++++
 internal/dnsforward/dnsforward.go             |  86 +++++----
 internal/dnsforward/dnsforward_test.go        |  92 +++------
 internal/dnsforward/filter.go                 |   8 +-
 internal/dnsforward/http.go                   |   9 +-
 internal/dnsforward/{dns.go => process.go}    |  63 ++++---
 .../{dns_test.go => process_internal_test.go} | 123 ++++++++++--
 internal/dnsforward/upstreams.go              |  10 +-
 internal/home/clients.go                      |  41 +++-
 ...ients_test.go => clients_internal_test.go} |  16 +-
 internal/home/config.go                       |   8 +-
 internal/home/dns.go                          | 177 +++---------------
 internal/home/home.go                         |  88 +--------
 internal/home/httpclient.go                   |  47 +++++
 16 files changed, 443 insertions(+), 397 deletions(-)
 create mode 100644 internal/dnsforward/dialcontext.go
 rename internal/dnsforward/{dns.go => process.go} (94%)
 rename internal/dnsforward/{dns_test.go => process_internal_test.go} (87%)
 rename internal/home/{clients_test.go => clients_internal_test.go} (94%)
 create mode 100644 internal/home/httpclient.go

diff --git a/CHANGELOG.md b/CHANGELOG.md
index fb6c12b1..3c43ed5c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,8 @@ NOTE: Add new changes BELOW THIS COMMENT.
 
 ### Fixed
 
+- Occasional client information lookup failures that could lead to the DNS
+  server getting stuck ([#6006]).
 - `bufio.Scanner: token too long` and other errors when trying to add
   filtering-rule lists with lines over 1024 bytes long or containing cosmetic
   rules ([#6003]).
@@ -35,6 +37,7 @@ NOTE: Add new changes BELOW THIS COMMENT.
   the `Dockerfile`.
 
 [#6003]: https://github.com/AdguardTeam/AdGuardHome/issues/6003
+[#6006]: https://github.com/AdguardTeam/AdGuardHome/issues/6006
 
 <!--
 NOTE: Add new changes ABOVE THIS COMMENT.
diff --git a/internal/dnsforward/config.go b/internal/dnsforward/config.go
index aa3f4808..20bc9770 100644
--- a/internal/dnsforward/config.go
+++ b/internal/dnsforward/config.go
@@ -13,6 +13,7 @@ import (
 	"github.com/AdguardTeam/AdGuardHome/internal/aghalg"
 	"github.com/AdguardTeam/AdGuardHome/internal/aghhttp"
 	"github.com/AdguardTeam/AdGuardHome/internal/aghtls"
+	"github.com/AdguardTeam/AdGuardHome/internal/client"
 	"github.com/AdguardTeam/AdGuardHome/internal/filtering"
 	"github.com/AdguardTeam/dnsproxy/proxy"
 	"github.com/AdguardTeam/golibs/errors"
@@ -270,7 +271,13 @@ type ServerConfig struct {
 	UDPListenAddrs []*net.UDPAddr        // UDP listen address
 	TCPListenAddrs []*net.TCPAddr        // TCP listen address
 	UpstreamConfig *proxy.UpstreamConfig // Upstream DNS servers config
-	OnDNSRequest   func(d *proxy.DNSContext)
+
+	// AddrProcConf defines the configuration for the client IP processor.
+	// If nil, [client.EmptyAddrProc] is used.
+	//
+	// TODO(a.garipov): The use of [client.EmptyAddrProc] is a crutch for tests.
+	// Remove that.
+	AddrProcConf *client.DefaultAddrProcConfig
 
 	FilteringConfig
 	TLSConfig
@@ -298,9 +305,6 @@ type ServerConfig struct {
 	// DNS64Prefixes is a slice of NAT64 prefixes to be used for DNS64.
 	DNS64Prefixes []netip.Prefix
 
-	// ResolveClients signals if the RDNS should resolve clients' addresses.
-	ResolveClients bool
-
 	// UsePrivateRDNS defines if the PTR requests for unknown addresses from
 	// locally-served networks should be resolved via private PTR resolvers.
 	UsePrivateRDNS bool
diff --git a/internal/dnsforward/dialcontext.go b/internal/dnsforward/dialcontext.go
new file mode 100644
index 00000000..db32dd3d
--- /dev/null
+++ b/internal/dnsforward/dialcontext.go
@@ -0,0 +1,57 @@
+package dnsforward
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"time"
+
+	"github.com/AdguardTeam/golibs/errors"
+	"github.com/AdguardTeam/golibs/log"
+)
+
+// DialContext is a [whois.DialContextFunc] that uses s to resolve hostnames.
+func (s *Server) DialContext(ctx context.Context, network, addr string) (conn net.Conn, err error) {
+	log.Debug("dnsforward: dialing %q for network %q", addr, network)
+
+	host, port, err := net.SplitHostPort(addr)
+	if err != nil {
+		return nil, err
+	}
+
+	dialer := &net.Dialer{
+		// TODO(a.garipov): Consider making configurable.
+		Timeout: time.Minute * 5,
+	}
+
+	if net.ParseIP(host) != nil {
+		return dialer.DialContext(ctx, network, addr)
+	}
+
+	addrs, err := s.Resolve(host)
+	if err != nil {
+		return nil, fmt.Errorf("resolving %q: %w", host, err)
+	}
+
+	log.Debug("dnsforward: resolving %q: %v", host, addrs)
+
+	if len(addrs) == 0 {
+		return nil, fmt.Errorf("no addresses for host %q", host)
+	}
+
+	var dialErrs []error
+	for _, a := range addrs {
+		addr = net.JoinHostPort(a.String(), port)
+		conn, err = dialer.DialContext(ctx, network, addr)
+		if err != nil {
+			dialErrs = append(dialErrs, err)
+
+			continue
+		}
+
+		return conn, err
+	}
+
+	// TODO(a.garipov): Use errors.Join in Go 1.20.
+	return nil, errors.List(fmt.Sprintf("dialing %q", addr), dialErrs...)
+}
diff --git a/internal/dnsforward/dnsforward.go b/internal/dnsforward/dnsforward.go
index 70abd660..bb389969 100644
--- a/internal/dnsforward/dnsforward.go
+++ b/internal/dnsforward/dnsforward.go
@@ -14,6 +14,7 @@ import (
 
 	"github.com/AdguardTeam/AdGuardHome/internal/aghalg"
 	"github.com/AdguardTeam/AdGuardHome/internal/aghnet"
+	"github.com/AdguardTeam/AdGuardHome/internal/client"
 	"github.com/AdguardTeam/AdGuardHome/internal/dhcpd"
 	"github.com/AdguardTeam/AdGuardHome/internal/filtering"
 	"github.com/AdguardTeam/AdGuardHome/internal/querylog"
@@ -99,6 +100,10 @@ type Server struct {
 	// must be a valid domain name plus dots on each side.
 	localDomainSuffix string
 
+	// addrProc, if not nil, is used to process clients' IP addresses with rDNS,
+	// WHOIS, etc.
+	addrProc client.AddressProcessor
+
 	ipset          ipsetCtx
 	privateNets    netutil.SubnetSet
 	localResolvers *proxy.Proxy
@@ -170,6 +175,9 @@ const (
 
 // NewServer creates a new instance of the dnsforward.Server
 // Note: this function must be called only once
+//
+// TODO(a.garipov): How many constructors and initializers does this thing have?
+// Refactor!
 func NewServer(p DNSCreateParams) (s *Server, err error) {
 	var localDomainSuffix string
 	if p.LocalDomain == "" {
@@ -257,14 +265,25 @@ func (s *Server) WriteDiskConfig(c *FilteringConfig) {
 	c.UpstreamDNS = stringutil.CloneSlice(sc.UpstreamDNS)
 }
 
-// RDNSSettings returns the copy of actual RDNS configuration.
-func (s *Server) RDNSSettings() (localPTRResolvers []string, resolveClients, resolvePTR bool) {
+// LocalPTRResolvers returns the current local PTR resolver configuration.
+func (s *Server) LocalPTRResolvers() (localPTRResolvers []string) {
 	s.serverLock.RLock()
 	defer s.serverLock.RUnlock()
 
-	return stringutil.CloneSlice(s.conf.LocalPTRResolvers),
-		s.conf.ResolveClients,
-		s.conf.UsePrivateRDNS
+	return stringutil.CloneSlice(s.conf.LocalPTRResolvers)
+}
+
+// AddrProcConfig returns the current address processing configuration.  Only
+// fields c.UsePrivateRDNS, c.UseRDNS, and c.UseWHOIS are filled.
+func (s *Server) AddrProcConfig() (c *client.DefaultAddrProcConfig) {
+	s.serverLock.RLock()
+	defer s.serverLock.RUnlock()
+
+	return &client.DefaultAddrProcConfig{
+		UsePrivateRDNS: s.conf.UsePrivateRDNS,
+		UseRDNS:        s.conf.AddrProcConf.UseRDNS,
+		UseWHOIS:       s.conf.AddrProcConf.UseWHOIS,
+	}
 }
 
 // Resolve - get IP addresses by host name from an upstream server.
@@ -296,10 +315,6 @@ func (s *Server) Exchange(ip netip.Addr) (host string, err error) {
 	s.serverLock.RLock()
 	defer s.serverLock.RUnlock()
 
-	if !s.conf.ResolveClients {
-		return "", nil
-	}
-
 	arpa, err := netutil.IPToReversedAddr(ip.AsSlice())
 	if err != nil {
 		return "", fmt.Errorf("reversing ip: %w", err)
@@ -318,14 +333,15 @@ func (s *Server) Exchange(ip netip.Addr) (host string, err error) {
 			Qclass: dns.ClassINET,
 		}},
 	}
-	ctx := &proxy.DNSContext{
+
+	dctx := &proxy.DNSContext{
 		Proto:     "udp",
 		Req:       req,
 		StartTime: time.Now(),
 	}
 
 	var resolver *proxy.Proxy
-	if s.isPrivateIP(ip) {
+	if s.privateNets.Contains(ip.AsSlice()) {
 		if !s.conf.UsePrivateRDNS {
 			return "", nil
 		}
@@ -336,11 +352,11 @@ func (s *Server) Exchange(ip netip.Addr) (host string, err error) {
 		resolver = s.internalProxy
 	}
 
-	if err = resolver.Resolve(ctx); err != nil {
+	if err = resolver.Resolve(dctx); err != nil {
 		return "", err
 	}
 
-	return hostFromPTR(ctx.Res)
+	return hostFromPTR(dctx.Res)
 }
 
 // hostFromPTR returns domain name from the PTR response or error.
@@ -364,27 +380,6 @@ func hostFromPTR(resp *dns.Msg) (host string, err error) {
 	return "", ErrRDNSNoData
 }
 
-// isPrivateIP returns true if the ip is private.
-func (s *Server) isPrivateIP(ip netip.Addr) (ok bool) {
-	return s.privateNets.Contains(ip.AsSlice())
-}
-
-// ShouldResolveClient returns false if ip is a loopback address, or ip is
-// private and resolving of private addresses is disabled.
-func (s *Server) ShouldResolveClient(ip netip.Addr) (ok bool) {
-	if ip.IsLoopback() {
-		return false
-	}
-
-	isPrivate := s.isPrivateIP(ip)
-
-	s.serverLock.RLock()
-	defer s.serverLock.RUnlock()
-
-	return s.conf.ResolveClients &&
-		(s.conf.UsePrivateRDNS || !isPrivate)
-}
-
 // Start starts the DNS server.
 func (s *Server) Start() error {
 	s.serverLock.Lock()
@@ -555,6 +550,24 @@ func (s *Server) Prepare(conf *ServerConfig) (err error) {
 
 	s.recDetector.clear()
 
+	if s.conf.AddrProcConf == nil {
+		// TODO(a.garipov): This is a crutch for tests; remove.
+		s.conf.AddrProcConf = &client.DefaultAddrProcConfig{}
+		s.addrProc = client.EmptyAddrProc{}
+	} else {
+		c := s.conf.AddrProcConf
+		c.DialContext = s.DialContext
+		c.PrivateSubnets = s.privateNets
+		c.UsePrivateRDNS = s.conf.UsePrivateRDNS
+		s.addrProc = client.NewDefaultAddrProc(s.conf.AddrProcConf)
+
+		// Clear the initial addresses to not resolve them again.
+		//
+		// TODO(a.garipov): Consider ways of removing this once more client
+		// logic is moved to package client.
+		c.InitialAddresses = nil
+	}
+
 	return nil
 }
 
@@ -696,6 +709,11 @@ func (s *Server) Reconfigure(conf *ServerConfig) error {
 	// TODO(a.garipov): This whole piece of API is weird and needs to be remade.
 	if conf == nil {
 		conf = &s.conf
+	} else {
+		closeErr := s.addrProc.Close()
+		if closeErr != nil {
+			log.Error("dnsforward: closing address processor: %s", closeErr)
+		}
 	}
 
 	err = s.Prepare(conf)
diff --git a/internal/dnsforward/dnsforward_test.go b/internal/dnsforward/dnsforward_test.go
index 705227a1..bbb42116 100644
--- a/internal/dnsforward/dnsforward_test.go
+++ b/internal/dnsforward/dnsforward_test.go
@@ -39,11 +39,29 @@ func TestMain(m *testing.M) {
 	testutil.DiscardLogOutput(m)
 }
 
+// testTimeout is the common timeout for tests.
+//
+// TODO(a.garipov): Use more.
+const testTimeout = 1 * time.Second
+
+// testQuestionTarget is the common question target for tests.
+//
+// TODO(a.garipov): Use more.
+const testQuestionTarget = "target.example"
+
 const (
 	tlsServerName     = "testdns.adguard.com"
 	testMessagesCount = 10
 )
 
+// testClientAddr is the common net.Addr for tests.
+//
+// TODO(a.garipov): Use more.
+var testClientAddr net.Addr = &net.TCPAddr{
+	IP:   net.IP{1, 2, 3, 4},
+	Port: 12345,
+}
+
 func startDeferStop(t *testing.T, s *Server) {
 	t.Helper()
 
@@ -53,6 +71,13 @@ func startDeferStop(t *testing.T, s *Server) {
 	testutil.CleanupAndRequireSuccess(t, s.Stop)
 }
 
+// packageUpstreamVariableMu is used to serialize access to the package-level
+// variables of package upstream.
+//
+// TODO(s.chzhen): Move these parameters to upstream options and remove this
+// crutch.
+var packageUpstreamVariableMu = &sync.Mutex{}
+
 func createTestServer(
 	t *testing.T,
 	filterConf *filtering.Config,
@@ -61,6 +86,9 @@ func createTestServer(
 ) (s *Server) {
 	t.Helper()
 
+	packageUpstreamVariableMu.Lock()
+	defer packageUpstreamVariableMu.Unlock()
+
 	rules := `||nxdomain.example.org
 ||NULL.example.org^
 127.0.0.1	host.example.org
@@ -307,11 +335,9 @@ func TestServer(t *testing.T) {
 }
 
 func TestServer_timeout(t *testing.T) {
-	const timeout time.Duration = time.Second
-
 	t.Run("custom", func(t *testing.T) {
 		srvConf := &ServerConfig{
-			UpstreamTimeout: timeout,
+			UpstreamTimeout: testTimeout,
 			FilteringConfig: FilteringConfig{
 				BlockingMode:     BlockingModeDefault,
 				EDNSClientSubnet: &EDNSClientSubnet{Enabled: false},
@@ -324,7 +350,7 @@ func TestServer_timeout(t *testing.T) {
 		err = s.Prepare(srvConf)
 		require.NoError(t, err)
 
-		assert.Equal(t, timeout, s.conf.UpstreamTimeout)
+		assert.Equal(t, testTimeout, s.conf.UpstreamTimeout)
 	})
 
 	t.Run("default", func(t *testing.T) {
@@ -545,7 +571,7 @@ func TestInvalidRequest(t *testing.T) {
 
 	// Send a DNS request without question.
 	_, _, err := (&dns.Client{
-		Timeout: 500 * time.Millisecond,
+		Timeout: testTimeout,
 	}).Exchange(&req, addr)
 
 	assert.NoErrorf(t, err, "got a response to an invalid query")
@@ -1320,9 +1346,7 @@ func TestServer_Exchange(t *testing.T) {
 		},
 	}
 
-	srv.conf.ResolveClients = true
 	srv.conf.UsePrivateRDNS = true
-
 	srv.privateNets = netutil.SubnetSetFunc(netutil.IsLocallyServed)
 
 	testCases := []struct {
@@ -1396,57 +1420,3 @@ func TestServer_Exchange(t *testing.T) {
 		assert.Empty(t, host)
 	})
 }
-
-func TestServer_ShouldResolveClient(t *testing.T) {
-	srv := &Server{
-		privateNets: netutil.SubnetSetFunc(netutil.IsLocallyServed),
-	}
-
-	testCases := []struct {
-		ip         netip.Addr
-		want       require.BoolAssertionFunc
-		name       string
-		resolve    bool
-		usePrivate bool
-	}{{
-		name:       "default",
-		ip:         netip.MustParseAddr("1.1.1.1"),
-		want:       require.True,
-		resolve:    true,
-		usePrivate: true,
-	}, {
-		name:       "no_rdns",
-		ip:         netip.MustParseAddr("1.1.1.1"),
-		want:       require.False,
-		resolve:    false,
-		usePrivate: true,
-	}, {
-		name:       "loopback",
-		ip:         netip.MustParseAddr("127.0.0.1"),
-		want:       require.False,
-		resolve:    true,
-		usePrivate: true,
-	}, {
-		name:       "private_resolve",
-		ip:         netip.MustParseAddr("192.168.0.1"),
-		want:       require.True,
-		resolve:    true,
-		usePrivate: true,
-	}, {
-		name:       "private_no_resolve",
-		ip:         netip.MustParseAddr("192.168.0.1"),
-		want:       require.False,
-		resolve:    true,
-		usePrivate: false,
-	}}
-
-	for _, tc := range testCases {
-		t.Run(tc.name, func(t *testing.T) {
-			srv.conf.ResolveClients = tc.resolve
-			srv.conf.UsePrivateRDNS = tc.usePrivate
-
-			ok := srv.ShouldResolveClient(tc.ip)
-			tc.want(t, ok)
-		})
-	}
-}
diff --git a/internal/dnsforward/filter.go b/internal/dnsforward/filter.go
index f55e3059..3f35afc2 100644
--- a/internal/dnsforward/filter.go
+++ b/internal/dnsforward/filter.go
@@ -50,10 +50,10 @@ func (s *Server) beforeRequestHandler(
 	return true, nil
 }
 
-// getClientRequestFilteringSettings looks up client filtering settings using
-// the client's IP address and ID, if any, from dctx.
-func (s *Server) getClientRequestFilteringSettings(dctx *dnsContext) *filtering.Settings {
-	setts := s.dnsFilter.Settings()
+// clientRequestFilteringSettings looks up client filtering settings using the
+// client's IP address and ID, if any, from dctx.
+func (s *Server) clientRequestFilteringSettings(dctx *dnsContext) (setts *filtering.Settings) {
+	setts = s.dnsFilter.Settings()
 	setts.ProtectionEnabled = dctx.protectionEnabled
 	if s.conf.FilterHandler != nil {
 		ip, _ := netutil.IPAndPortFromAddr(dctx.proxyCtx.Addr)
diff --git a/internal/dnsforward/http.go b/internal/dnsforward/http.go
index e95459c7..761cbeb4 100644
--- a/internal/dnsforward/http.go
+++ b/internal/dnsforward/http.go
@@ -124,7 +124,7 @@ func (s *Server) getDNSConfig() (c *jsonDNSConfig) {
 	cacheMinTTL := s.conf.CacheMinTTL
 	cacheMaxTTL := s.conf.CacheMaxTTL
 	cacheOptimistic := s.conf.CacheOptimistic
-	resolveClients := s.conf.ResolveClients
+	resolveClients := s.conf.AddrProcConf.UseRDNS
 	usePrivateRDNS := s.conf.UsePrivateRDNS
 	localPTRUpstreams := stringutil.CloneSliceOrEmpty(s.conf.LocalPTRResolvers)
 
@@ -314,8 +314,6 @@ func (s *Server) setConfig(dc *jsonDNSConfig) (shouldRestart bool) {
 	setIfNotNil(&s.conf.ProtectionEnabled, dc.ProtectionEnabled)
 	setIfNotNil(&s.conf.EnableDNSSEC, dc.DNSSECEnabled)
 	setIfNotNil(&s.conf.AAAADisabled, dc.DisableIPv6)
-	setIfNotNil(&s.conf.ResolveClients, dc.ResolveClients)
-	setIfNotNil(&s.conf.UsePrivateRDNS, dc.UsePrivateRDNS)
 
 	return s.setConfigRestartable(dc)
 }
@@ -335,6 +333,9 @@ func setIfNotNil[T any](currentPtr, newPtr *T) (hasSet bool) {
 // setConfigRestartable sets the parameters which trigger a restart.
 // shouldRestart is true if the server should be restarted to apply changes.
 // s.serverLock is expected to be locked.
+//
+// TODO(a.garipov): Some of these could probably be updated without a restart.
+// Inspect and consider refactoring.
 func (s *Server) setConfigRestartable(dc *jsonDNSConfig) (shouldRestart bool) {
 	for _, hasSet := range []bool{
 		setIfNotNil(&s.conf.UpstreamDNS, dc.Upstreams),
@@ -347,6 +348,8 @@ func (s *Server) setConfigRestartable(dc *jsonDNSConfig) (shouldRestart bool) {
 		setIfNotNil(&s.conf.CacheMinTTL, dc.CacheMinTTL),
 		setIfNotNil(&s.conf.CacheMaxTTL, dc.CacheMaxTTL),
 		setIfNotNil(&s.conf.CacheOptimistic, dc.CacheOptimistic),
+		setIfNotNil(&s.conf.AddrProcConf.UseRDNS, dc.ResolveClients),
+		setIfNotNil(&s.conf.UsePrivateRDNS, dc.UsePrivateRDNS),
 	} {
 		shouldRestart = shouldRestart || hasSet
 		if shouldRestart {
diff --git a/internal/dnsforward/dns.go b/internal/dnsforward/process.go
similarity index 94%
rename from internal/dnsforward/dns.go
rename to internal/dnsforward/process.go
index 6007801f..e6949ec1 100644
--- a/internal/dnsforward/dns.go
+++ b/internal/dnsforward/process.go
@@ -30,6 +30,7 @@ type dnsContext struct {
 	setts *filtering.Settings
 
 	result *filtering.Result
+
 	// origResp is the response received from upstream.  It is set when the
 	// response is modified by filters.
 	origResp *dns.Msg
@@ -48,13 +49,13 @@ type dnsContext struct {
 	// clientID is the ClientID from DoH, DoQ, or DoT, if provided.
 	clientID string
 
+	// startTime is the time at which the processing of the request has started.
+	startTime time.Time
+
 	// origQuestion is the question received from the client.  It is set
 	// when the request is modified by rewrites.
 	origQuestion dns.Question
 
-	// startTime is the time at which the processing of the request has started.
-	startTime time.Time
-
 	// protectionEnabled shows if the filtering is enabled, and if the
 	// server's DNS filter is ready.
 	protectionEnabled bool
@@ -160,6 +161,22 @@ func (s *Server) processRecursion(dctx *dnsContext) (rc resultCode) {
 	return resultCodeSuccess
 }
 
+// mozillaFQDN is the domain used to signal the Firefox browser to not use its
+// own DoH server.
+//
+// See https://support.mozilla.org/en-US/kb/canary-domain-use-application-dnsnet.
+const mozillaFQDN = "use-application-dns.net."
+
+// healthcheckFQDN is a reserved domain-name used for healthchecking.
+//
+// [Section 6.2 of RFC 6761] states that DNS Registries/Registrars must not
+// grant requests to register test names in the normal way to any person or
+// entity, making domain names under the .test TLD free to use in internal
+// purposes.
+//
+// [Section 6.2 of RFC 6761]: https://www.rfc-editor.org/rfc/rfc6761.html#section-6.2
+const healthcheckFQDN = "healthcheck.adguardhome.test."
+
 // processInitial terminates the following processing for some requests if
 // needed and enriches dctx with some client-specific information.
 //
@@ -169,6 +186,8 @@ func (s *Server) processInitial(dctx *dnsContext) (rc resultCode) {
 	defer log.Debug("dnsforward: finished processing initial")
 
 	pctx := dctx.proxyCtx
+	s.processClientIP(pctx.Addr)
+
 	q := pctx.Req.Question[0]
 	qt := q.Qtype
 	if s.conf.AAAADisabled && qt == dns.TypeAAAA {
@@ -177,28 +196,13 @@ func (s *Server) processInitial(dctx *dnsContext) (rc resultCode) {
 		return resultCodeFinish
 	}
 
-	if s.conf.OnDNSRequest != nil {
-		s.conf.OnDNSRequest(pctx)
-	}
-
-	// Disable Mozilla DoH.
-	//
-	// See https://support.mozilla.org/en-US/kb/canary-domain-use-application-dnsnet.
-	if (qt == dns.TypeA || qt == dns.TypeAAAA) && q.Name == "use-application-dns.net." {
+	if (qt == dns.TypeA || qt == dns.TypeAAAA) && q.Name == mozillaFQDN {
 		pctx.Res = s.genNXDomain(pctx.Req)
 
 		return resultCodeFinish
 	}
 
-	// Handle a reserved domain healthcheck.adguardhome.test.
-	//
-	// [Section 6.2 of RFC 6761] states that DNS Registries/Registrars must not
-	// grant requests to register test names in the normal way to any person or
-	// entity, making domain names under test. TLD free to use in internal
-	// purposes.
-	//
-	// [Section 6.2 of RFC 6761]: https://www.rfc-editor.org/rfc/rfc6761.html#section-6.2
-	if q.Name == "healthcheck.adguardhome.test." {
+	if q.Name == healthcheckFQDN {
 		// Generate a NODATA negative response to make nslookup exit with 0.
 		pctx.Res = s.makeResponse(pctx.Req)
 
@@ -213,11 +217,28 @@ func (s *Server) processInitial(dctx *dnsContext) (rc resultCode) {
 
 	// Get the client-specific filtering settings.
 	dctx.protectionEnabled, _ = s.UpdatedProtectionStatus()
-	dctx.setts = s.getClientRequestFilteringSettings(dctx)
+	dctx.setts = s.clientRequestFilteringSettings(dctx)
 
 	return resultCodeSuccess
 }
 
+// processClientIP sends the client IP address to s.addrProc, if needed.
+func (s *Server) processClientIP(addr net.Addr) {
+	clientIP := netutil.NetAddrToAddrPort(addr).Addr()
+	if clientIP == (netip.Addr{}) {
+		log.Info("dnsforward: warning: bad client addr %q", addr)
+
+		return
+	}
+
+	// Do not assign s.addrProc to a local variable to then use, since this lock
+	// also serializes the closure of s.addrProc.
+	s.serverLock.RLock()
+	defer s.serverLock.RUnlock()
+
+	s.addrProc.Process(clientIP)
+}
+
 func (s *Server) setTableHostToIP(t hostToIPTable) {
 	s.tableHostToIPLock.Lock()
 	defer s.tableHostToIPLock.Unlock()
diff --git a/internal/dnsforward/dns_test.go b/internal/dnsforward/process_internal_test.go
similarity index 87%
rename from internal/dnsforward/dns_test.go
rename to internal/dnsforward/process_internal_test.go
index 1bcca756..a45ce245 100644
--- a/internal/dnsforward/dns_test.go
+++ b/internal/dnsforward/process_internal_test.go
@@ -12,6 +12,7 @@ import (
 	"github.com/AdguardTeam/dnsproxy/upstream"
 	"github.com/AdguardTeam/golibs/netutil"
 	"github.com/AdguardTeam/golibs/testutil"
+	"github.com/AdguardTeam/urlfilter/rules"
 	"github.com/miekg/dns"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -22,6 +23,96 @@ const (
 	ddrTestFQDN       = ddrTestDomainName + "."
 )
 
+func TestServer_ProcessInitial(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name         string
+		target       string
+		wantRCode    rules.RCode
+		qType        rules.RRType
+		aaaaDisabled bool
+		wantRC       resultCode
+	}{{
+		name:         "success",
+		target:       testQuestionTarget,
+		wantRCode:    -1,
+		qType:        dns.TypeA,
+		aaaaDisabled: false,
+		wantRC:       resultCodeSuccess,
+	}, {
+		name:         "aaaa_disabled",
+		target:       testQuestionTarget,
+		wantRCode:    dns.RcodeSuccess,
+		qType:        dns.TypeAAAA,
+		aaaaDisabled: true,
+		wantRC:       resultCodeFinish,
+	}, {
+		name:         "aaaa_disabled_a",
+		target:       testQuestionTarget,
+		wantRCode:    -1,
+		qType:        dns.TypeA,
+		aaaaDisabled: true,
+		wantRC:       resultCodeSuccess,
+	}, {
+		name:         "mozilla_canary",
+		target:       mozillaFQDN,
+		wantRCode:    dns.RcodeNameError,
+		qType:        dns.TypeA,
+		aaaaDisabled: false,
+		wantRC:       resultCodeFinish,
+	}, {
+		name:         "adguardhome_healthcheck",
+		target:       healthcheckFQDN,
+		wantRCode:    dns.RcodeSuccess,
+		qType:        dns.TypeA,
+		aaaaDisabled: false,
+		wantRC:       resultCodeFinish,
+	}}
+
+	for _, tc := range testCases {
+		tc := tc
+
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			c := ServerConfig{
+				FilteringConfig: FilteringConfig{
+					AAAADisabled:     tc.aaaaDisabled,
+					EDNSClientSubnet: &EDNSClientSubnet{Enabled: false},
+				},
+			}
+
+			s := createTestServer(t, &filtering.Config{}, c, nil)
+
+			var gotAddr netip.Addr
+			s.addrProc = &aghtest.AddressProcessor{
+				OnProcess: func(ip netip.Addr) { gotAddr = ip },
+				OnClose:   func() (err error) { panic("not implemented") },
+			}
+
+			dctx := &dnsContext{
+				proxyCtx: &proxy.DNSContext{
+					Req:       createTestMessageWithType(tc.target, tc.qType),
+					Addr:      testClientAddr,
+					RequestID: 1234,
+				},
+			}
+
+			gotRC := s.processInitial(dctx)
+			assert.Equal(t, tc.wantRC, gotRC)
+			assert.Equal(t, netutil.NetAddrToAddrPort(testClientAddr).Addr(), gotAddr)
+
+			if tc.wantRCode > 0 {
+				gotResp := dctx.proxyCtx.Res
+				require.NotNil(t, gotResp)
+
+				assert.Equal(t, tc.wantRCode, gotResp.Rcode)
+			}
+		})
+	}
+}
+
 func TestServer_ProcessDDRQuery(t *testing.T) {
 	dohSVCB := &dns.SVCB{
 		Priority: 1,
@@ -64,7 +155,7 @@ func TestServer_ProcessDDRQuery(t *testing.T) {
 	}{{
 		name:       "pass_host",
 		wantRes:    resultCodeSuccess,
-		host:       "example.net.",
+		host:       testQuestionTarget,
 		qtype:      dns.TypeSVCB,
 		ddrEnabled: true,
 		portDoH:    8043,
@@ -234,33 +325,33 @@ func TestServer_ProcessDetermineLocal(t *testing.T) {
 func TestServer_ProcessDHCPHosts_localRestriction(t *testing.T) {
 	knownIP := netip.MustParseAddr("1.2.3.4")
 	testCases := []struct {
+		wantIP     netip.Addr
 		name       string
 		host       string
-		wantIP     netip.Addr
 		wantRes    resultCode
 		isLocalCli bool
 	}{{
+		wantIP:     knownIP,
 		name:       "local_client_success",
 		host:       "example.lan",
-		wantIP:     knownIP,
 		wantRes:    resultCodeSuccess,
 		isLocalCli: true,
 	}, {
+		wantIP:     netip.Addr{},
 		name:       "local_client_unknown_host",
 		host:       "wronghost.lan",
-		wantIP:     netip.Addr{},
 		wantRes:    resultCodeSuccess,
 		isLocalCli: true,
 	}, {
+		wantIP:     netip.Addr{},
 		name:       "external_client_known_host",
 		host:       "example.lan",
-		wantIP:     netip.Addr{},
 		wantRes:    resultCodeFinish,
 		isLocalCli: false,
 	}, {
+		wantIP:     netip.Addr{},
 		name:       "external_client_unknown_host",
 		host:       "wronghost.lan",
-		wantIP:     netip.Addr{},
 		wantRes:    resultCodeFinish,
 		isLocalCli: false,
 	}}
@@ -332,52 +423,52 @@ func TestServer_ProcessDHCPHosts(t *testing.T) {
 
 	knownIP := netip.MustParseAddr("1.2.3.4")
 	testCases := []struct {
+		wantIP  netip.Addr
 		name    string
 		host    string
 		suffix  string
-		wantIP  netip.Addr
 		wantRes resultCode
 		qtyp    uint16
 	}{{
+		wantIP:  netip.Addr{},
 		name:    "success_external",
 		host:    examplecom,
 		suffix:  defaultLocalDomainSuffix,
-		wantIP:  netip.Addr{},
 		wantRes: resultCodeSuccess,
 		qtyp:    dns.TypeA,
 	}, {
+		wantIP:  netip.Addr{},
 		name:    "success_external_non_a",
 		host:    examplecom,
 		suffix:  defaultLocalDomainSuffix,
-		wantIP:  netip.Addr{},
 		wantRes: resultCodeSuccess,
 		qtyp:    dns.TypeCNAME,
 	}, {
+		wantIP:  knownIP,
 		name:    "success_internal",
 		host:    examplelan,
 		suffix:  defaultLocalDomainSuffix,
-		wantIP:  knownIP,
 		wantRes: resultCodeSuccess,
 		qtyp:    dns.TypeA,
 	}, {
+		wantIP:  netip.Addr{},
 		name:    "success_internal_unknown",
 		host:    "example-new.lan",
 		suffix:  defaultLocalDomainSuffix,
-		wantIP:  netip.Addr{},
 		wantRes: resultCodeSuccess,
 		qtyp:    dns.TypeA,
 	}, {
+		wantIP:  netip.Addr{},
 		name:    "success_internal_aaaa",
 		host:    examplelan,
 		suffix:  defaultLocalDomainSuffix,
-		wantIP:  netip.Addr{},
 		wantRes: resultCodeSuccess,
 		qtyp:    dns.TypeAAAA,
 	}, {
+		wantIP:  knownIP,
 		name:    "success_custom_suffix",
 		host:    "example.custom",
 		suffix:  "custom",
-		wantIP:  knownIP,
 		wantRes: resultCodeSuccess,
 		qtyp:    dns.TypeA,
 	}}
@@ -560,10 +651,8 @@ func TestServer_ProcessLocalPTR_usingResolvers(t *testing.T) {
 	var dnsCtx *dnsContext
 	setup := func(use bool) {
 		proxyCtx = &proxy.DNSContext{
-			Addr: &net.TCPAddr{
-				IP: net.IP{127, 0, 0, 1},
-			},
-			Req: createTestMessageWithType(reqAddr, dns.TypePTR),
+			Addr: testClientAddr,
+			Req:  createTestMessageWithType(reqAddr, dns.TypePTR),
 		}
 		dnsCtx = &dnsContext{
 			proxyCtx:        proxyCtx,
diff --git a/internal/dnsforward/upstreams.go b/internal/dnsforward/upstreams.go
index cbd92b36..ceec1cb7 100644
--- a/internal/dnsforward/upstreams.go
+++ b/internal/dnsforward/upstreams.go
@@ -42,11 +42,13 @@ func (s *Server) loadUpstreams() (upstreams []string, err error) {
 
 // prepareUpstreamSettings sets upstream DNS server settings.
 func (s *Server) prepareUpstreamSettings() (err error) {
-	// We're setting a customized set of RootCAs.  The reason is that Go default
-	// mechanism of loading TLS roots does not always work properly on some
-	// routers so we're loading roots manually and pass it here.
+	// Use a customized set of RootCAs, because Go's default mechanism of
+	// loading TLS roots does not always work properly on some routers so we're
+	// loading roots manually and pass it here.
 	//
 	// See [aghtls.SystemRootCAs].
+	//
+	// TODO(a.garipov): Investigate if that's true.
 	upstream.RootCAs = s.conf.TLSv12Roots
 	upstream.CipherSuites = s.conf.TLSCiphers
 
@@ -190,7 +192,7 @@ func (s *Server) resolveUpstreamsWithHosts(
 
 // extractUpstreamHost returns the hostname of addr without port with an
 // assumption that any address passed here has already been successfully parsed
-// by [upstream.AddressToUpstream].  This function eesentially mirrors the logic
+// by [upstream.AddressToUpstream].  This function essentially mirrors the logic
 // of [upstream.AddressToUpstream], see TODO on [replaceUpstreamsWithHosts].
 func extractUpstreamHost(addr string) (host string) {
 	var err error
diff --git a/internal/home/clients.go b/internal/home/clients.go
index 1cd3add0..049710bc 100644
--- a/internal/home/clients.go
+++ b/internal/home/clients.go
@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/AdguardTeam/AdGuardHome/internal/aghnet"
+	"github.com/AdguardTeam/AdGuardHome/internal/client"
 	"github.com/AdguardTeam/AdGuardHome/internal/dhcpd"
 	"github.com/AdguardTeam/AdGuardHome/internal/dhcpsvc"
 	"github.com/AdguardTeam/AdGuardHome/internal/dnsforward"
@@ -141,7 +142,7 @@ func (clients *clientsContainer) handleHostsUpdates() {
 	}
 }
 
-// webHandlersRegistered prevents a [clientsContainer] from regisering its web
+// webHandlersRegistered prevents a [clientsContainer] from registering its web
 // handlers more than once.
 //
 // TODO(a.garipov): Refactor HTTP handler registration logic.
@@ -743,11 +744,9 @@ func (clients *clientsContainer) Update(prev, c *Client) (err error) {
 	return nil
 }
 
-// setWHOISInfo sets the WHOIS information for a client.
+// setWHOISInfo sets the WHOIS information for a client.  clients.lock is
+// expected to be locked.
 func (clients *clientsContainer) setWHOISInfo(ip netip.Addr, wi *whois.Info) {
-	clients.lock.Lock()
-	defer clients.lock.Unlock()
-
 	_, ok := clients.findLocked(ip.String())
 	if ok {
 		log.Debug("clients: client for %s is already created, ignore whois info", ip)
@@ -774,9 +773,11 @@ func (clients *clientsContainer) setWHOISInfo(ip netip.Addr, wi *whois.Info) {
 	rc.WHOIS = wi
 }
 
-// AddHost adds a new IP-hostname pairing.  The priorities of the sources are
+// addHost adds a new IP-hostname pairing.  The priorities of the sources are
 // taken into account.  ok is true if the pairing was added.
-func (clients *clientsContainer) AddHost(
+//
+// TODO(a.garipov): Only used in internal tests.  Consider removing.
+func (clients *clientsContainer) addHost(
 	ip netip.Addr,
 	host string,
 	src clientSource,
@@ -787,6 +788,32 @@ func (clients *clientsContainer) AddHost(
 	return clients.addHostLocked(ip, host, src)
 }
 
+// type check
+var _ client.AddressUpdater = (*clientsContainer)(nil)
+
+// UpdateAddress implements the [client.AddressUpdater] interface for
+// *clientsContainer
+func (clients *clientsContainer) UpdateAddress(ip netip.Addr, host string, info *whois.Info) {
+	// Common fast path optimization.
+	if host == "" && info == nil {
+		return
+	}
+
+	clients.lock.Lock()
+	defer clients.lock.Unlock()
+
+	if host != "" {
+		ok := clients.addHostLocked(ip, host, ClientSourceRDNS)
+		if !ok {
+			log.Debug("clients: host for client %q already set with higher priority source", ip)
+		}
+	}
+
+	if info != nil {
+		clients.setWHOISInfo(ip, info)
+	}
+}
+
 // addHostLocked adds a new IP-hostname pairing.  clients.lock is expected to be
 // locked.
 func (clients *clientsContainer) addHostLocked(
diff --git a/internal/home/clients_test.go b/internal/home/clients_internal_test.go
similarity index 94%
rename from internal/home/clients_test.go
rename to internal/home/clients_internal_test.go
index 9ad819ec..d3ff2a57 100644
--- a/internal/home/clients_test.go
+++ b/internal/home/clients_internal_test.go
@@ -168,13 +168,13 @@ func TestClients(t *testing.T) {
 
 	t.Run("addhost_success", func(t *testing.T) {
 		ip := netip.MustParseAddr("1.1.1.1")
-		ok := clients.AddHost(ip, "host", ClientSourceARP)
+		ok := clients.addHost(ip, "host", ClientSourceARP)
 		assert.True(t, ok)
 
-		ok = clients.AddHost(ip, "host2", ClientSourceARP)
+		ok = clients.addHost(ip, "host2", ClientSourceARP)
 		assert.True(t, ok)
 
-		ok = clients.AddHost(ip, "host3", ClientSourceHostsFile)
+		ok = clients.addHost(ip, "host3", ClientSourceHostsFile)
 		assert.True(t, ok)
 
 		assert.Equal(t, clients.clientSource(ip), ClientSourceHostsFile)
@@ -182,18 +182,18 @@ func TestClients(t *testing.T) {
 
 	t.Run("dhcp_replaces_arp", func(t *testing.T) {
 		ip := netip.MustParseAddr("1.2.3.4")
-		ok := clients.AddHost(ip, "from_arp", ClientSourceARP)
+		ok := clients.addHost(ip, "from_arp", ClientSourceARP)
 		assert.True(t, ok)
 		assert.Equal(t, clients.clientSource(ip), ClientSourceARP)
 
-		ok = clients.AddHost(ip, "from_dhcp", ClientSourceDHCP)
+		ok = clients.addHost(ip, "from_dhcp", ClientSourceDHCP)
 		assert.True(t, ok)
 		assert.Equal(t, clients.clientSource(ip), ClientSourceDHCP)
 	})
 
 	t.Run("addhost_fail", func(t *testing.T) {
 		ip := netip.MustParseAddr("1.1.1.1")
-		ok := clients.AddHost(ip, "host1", ClientSourceRDNS)
+		ok := clients.addHost(ip, "host1", ClientSourceRDNS)
 		assert.False(t, ok)
 	})
 }
@@ -216,7 +216,7 @@ func TestClientsWHOIS(t *testing.T) {
 
 	t.Run("existing_auto-client", func(t *testing.T) {
 		ip := netip.MustParseAddr("1.1.1.1")
-		ok := clients.AddHost(ip, "host", ClientSourceRDNS)
+		ok := clients.addHost(ip, "host", ClientSourceRDNS)
 		assert.True(t, ok)
 
 		clients.setWHOISInfo(ip, whois)
@@ -259,7 +259,7 @@ func TestClientsAddExisting(t *testing.T) {
 		assert.True(t, ok)
 
 		// Now add an auto-client with the same IP.
-		ok = clients.AddHost(ip, "test", ClientSourceRDNS)
+		ok = clients.addHost(ip, "test", ClientSourceRDNS)
 		assert.True(t, ok)
 	})
 
diff --git a/internal/home/config.go b/internal/home/config.go
index 60cbe621..2830f59d 100644
--- a/internal/home/config.go
+++ b/internal/home/config.go
@@ -590,7 +590,13 @@ func (c *configuration) write() (err error) {
 		s.WriteDiskConfig(&c)
 		dns := &config.DNS
 		dns.FilteringConfig = c
-		dns.LocalPTRResolvers, config.Clients.Sources.RDNS, dns.UsePrivateRDNS = s.RDNSSettings()
+
+		dns.LocalPTRResolvers = s.LocalPTRResolvers()
+
+		addrProcConf := s.AddrProcConfig()
+		config.Clients.Sources.RDNS = addrProcConf.UseRDNS
+		config.Clients.Sources.WHOIS = addrProcConf.UseWHOIS
+		dns.UsePrivateRDNS = addrProcConf.UsePrivateRDNS
 	}
 
 	if Context.dhcpServer != nil {
diff --git a/internal/home/dns.go b/internal/home/dns.go
index fbbda423..7dfa8b85 100644
--- a/internal/home/dns.go
+++ b/internal/home/dns.go
@@ -13,14 +13,12 @@ import (
 	"github.com/AdguardTeam/AdGuardHome/internal/aghalg"
 	"github.com/AdguardTeam/AdGuardHome/internal/aghhttp"
 	"github.com/AdguardTeam/AdGuardHome/internal/aghnet"
+	"github.com/AdguardTeam/AdGuardHome/internal/client"
 	"github.com/AdguardTeam/AdGuardHome/internal/dhcpd"
 	"github.com/AdguardTeam/AdGuardHome/internal/dnsforward"
 	"github.com/AdguardTeam/AdGuardHome/internal/filtering"
 	"github.com/AdguardTeam/AdGuardHome/internal/querylog"
-	"github.com/AdguardTeam/AdGuardHome/internal/rdns"
 	"github.com/AdguardTeam/AdGuardHome/internal/stats"
-	"github.com/AdguardTeam/AdGuardHome/internal/whois"
-	"github.com/AdguardTeam/dnsproxy/proxy"
 	"github.com/AdguardTeam/golibs/errors"
 	"github.com/AdguardTeam/golibs/log"
 	"github.com/AdguardTeam/golibs/netutil"
@@ -135,7 +133,7 @@ func initDNSServer(
 		return fmt.Errorf("preparing set of private subnets: %w", err)
 	}
 
-	p := dnsforward.DNSCreateParams{
+	Context.dnsServer, err = dnsforward.NewServer(dnsforward.DNSCreateParams{
 		DNSFilter:   filters,
 		Stats:       sts,
 		QueryLog:    qlog,
@@ -143,9 +141,7 @@ func initDNSServer(
 		Anonymizer:  anonymizer,
 		LocalDomain: config.DHCP.LocalDomainName,
 		DHCPServer:  dhcpSrv,
-	}
-
-	Context.dnsServer, err = dnsforward.NewServer(p)
+	})
 	if err != nil {
 		closeDNSServer()
 
@@ -154,134 +150,23 @@ func initDNSServer(
 
 	Context.clients.dnsServer = Context.dnsServer
 
-	dnsConf, err := generateServerConfig(tlsConf, httpReg)
+	dnsConf, err := newServerConfig(tlsConf, httpReg)
 	if err != nil {
 		closeDNSServer()
 
-		return fmt.Errorf("generateServerConfig: %w", err)
+		return fmt.Errorf("newServerConfig: %w", err)
 	}
 
-	err = Context.dnsServer.Prepare(&dnsConf)
+	err = Context.dnsServer.Prepare(dnsConf)
 	if err != nil {
 		closeDNSServer()
 
 		return fmt.Errorf("dnsServer.Prepare: %w", err)
 	}
 
-	initRDNS()
-	initWHOIS()
-
 	return nil
 }
 
-const (
-	// defaultQueueSize is the size of queue of IPs for rDNS and WHOIS
-	// processing.
-	defaultQueueSize = 255
-
-	// defaultCacheSize is the maximum size of the cache for rDNS and WHOIS
-	// processing.  It must be greater than zero.
-	defaultCacheSize = 10_000
-
-	// defaultIPTTL is the Time to Live duration for IP addresses cached by
-	// rDNS and WHOIS.
-	defaultIPTTL = 1 * time.Hour
-)
-
-// initRDNS initializes the rDNS.
-func initRDNS() {
-	Context.rdnsCh = make(chan netip.Addr, defaultQueueSize)
-
-	// TODO(s.chzhen):  Add ability to disable it on dns server configuration
-	// update in [dnsforward] package.
-	r := rdns.New(&rdns.Config{
-		Exchanger: Context.dnsServer,
-		CacheSize: defaultCacheSize,
-		CacheTTL:  defaultIPTTL,
-	})
-
-	go processRDNS(r)
-}
-
-// processRDNS processes reverse DNS lookup queries.  It is intended to be used
-// as a goroutine.
-func processRDNS(r rdns.Interface) {
-	defer log.OnPanic("rdns")
-
-	for ip := range Context.rdnsCh {
-		ok := Context.dnsServer.ShouldResolveClient(ip)
-		if !ok {
-			continue
-		}
-
-		host, changed := r.Process(ip)
-		if host == "" || !changed {
-			continue
-		}
-
-		ok = Context.clients.AddHost(ip, host, ClientSourceRDNS)
-		if ok {
-			continue
-		}
-
-		log.Debug(
-			"dns: can't set rdns info for client %q: already set with higher priority source",
-			ip,
-		)
-	}
-}
-
-// initWHOIS initializes the WHOIS.
-//
-// TODO(s.chzhen):  Consider making configurable.
-func initWHOIS() {
-	const (
-		// defaultTimeout is the timeout for WHOIS requests.
-		defaultTimeout = 5 * time.Second
-
-		// defaultMaxConnReadSize is an upper limit in bytes for reading from
-		// net.Conn.
-		defaultMaxConnReadSize = 64 * 1024
-
-		// defaultMaxRedirects is the maximum redirects count.
-		defaultMaxRedirects = 5
-
-		// defaultMaxInfoLen is the maximum length of whois.Info fields.
-		defaultMaxInfoLen = 250
-	)
-
-	Context.whoisCh = make(chan netip.Addr, defaultQueueSize)
-
-	var w whois.Interface
-
-	if config.Clients.Sources.WHOIS {
-		w = whois.New(&whois.Config{
-			DialContext:     customDialContext,
-			ServerAddr:      whois.DefaultServer,
-			Port:            whois.DefaultPort,
-			Timeout:         defaultTimeout,
-			CacheSize:       defaultCacheSize,
-			MaxConnReadSize: defaultMaxConnReadSize,
-			MaxRedirects:    defaultMaxRedirects,
-			MaxInfoLen:      defaultMaxInfoLen,
-			CacheTTL:        defaultIPTTL,
-		})
-	} else {
-		w = whois.Empty{}
-	}
-
-	go func() {
-		defer log.OnPanic("whois")
-
-		for ip := range Context.whoisCh {
-			info, changed := w.Process(context.Background(), ip)
-			if info != nil && changed {
-				Context.clients.setWHOISInfo(ip, info)
-			}
-		}
-	}()
-}
-
 // parseSubnetSet parses a slice of subnets.  If the slice is empty, it returns
 // a subnet set that matches all locally served networks, see
 // [netutil.IsLocallyServed].
@@ -312,17 +197,6 @@ func isRunning() bool {
 	return Context.dnsServer != nil && Context.dnsServer.IsRunning()
 }
 
-func onDNSRequest(pctx *proxy.DNSContext) {
-	ip := netutil.NetAddrToAddrPort(pctx.Addr).Addr()
-	if ip == (netip.Addr{}) {
-		// This would be quite weird if we get here.
-		return
-	}
-
-	Context.rdnsCh <- ip
-	Context.whoisCh <- ip
-}
-
 func ipsToTCPAddrs(ips []netip.Addr, port int) (tcpAddrs []*net.TCPAddr) {
 	if ips == nil {
 		return nil
@@ -349,23 +223,35 @@ func ipsToUDPAddrs(ips []netip.Addr, port int) (udpAddrs []*net.UDPAddr) {
 	return udpAddrs
 }
 
-func generateServerConfig(
+func newServerConfig(
 	tlsConf *tlsConfigSettings,
 	httpReg aghhttp.RegisterFunc,
-) (newConf dnsforward.ServerConfig, err error) {
+) (newConf *dnsforward.ServerConfig, err error) {
 	dnsConf := config.DNS
 	hosts := aghalg.CoalesceSlice(dnsConf.BindHosts, []netip.Addr{netutil.IPv4Localhost()})
-	newConf = dnsforward.ServerConfig{
+
+	newConf = &dnsforward.ServerConfig{
 		UDPListenAddrs:  ipsToUDPAddrs(hosts, dnsConf.Port),
 		TCPListenAddrs:  ipsToTCPAddrs(hosts, dnsConf.Port),
 		FilteringConfig: dnsConf.FilteringConfig,
 		ConfigModified:  onConfigModified,
 		HTTPRegister:    httpReg,
-		OnDNSRequest:    onDNSRequest,
 		UseDNS64:        config.DNS.UseDNS64,
 		DNS64Prefixes:   config.DNS.DNS64Prefixes,
 	}
 
+	const initialClientsNum = 100
+
+	// Do not set DialContext, PrivateSubnets, and UsePrivateRDNS, because they
+	// are set by [dnsforward.Server.Prepare].
+	newConf.AddrProcConf = &client.DefaultAddrProcConfig{
+		Exchanger:        Context.dnsServer,
+		AddressUpdater:   &Context.clients,
+		InitialAddresses: Context.stats.TopClientsIP(initialClientsNum),
+		UseRDNS:          config.Clients.Sources.RDNS,
+		UseWHOIS:         config.Clients.Sources.WHOIS,
+	}
+
 	if tlsConf.Enabled {
 		newConf.TLSConfig = tlsConf.TLSConfig
 		newConf.TLSConfig.ServerName = tlsConf.ServerName
@@ -385,9 +271,9 @@ func generateServerConfig(
 		if tlsConf.PortDNSCrypt != 0 {
 			newConf.DNSCryptConfig, err = newDNSCrypt(hosts, *tlsConf)
 			if err != nil {
-				// Don't wrap the error, because it's already
-				// wrapped by newDNSCrypt.
-				return dnsforward.ServerConfig{}, err
+				// Don't wrap the error, because it's already wrapped by
+				// newDNSCrypt.
+				return nil, err
 			}
 		}
 	}
@@ -401,7 +287,6 @@ func generateServerConfig(
 	newConf.LocalPTRResolvers = dnsConf.LocalPTRResolvers
 	newConf.UpstreamTimeout = dnsConf.UpstreamTimeout.Duration
 
-	newConf.ResolveClients = config.Clients.Sources.RDNS
 	newConf.UsePrivateRDNS = dnsConf.UsePrivateRDNS
 	newConf.ServeHTTP3 = dnsConf.ServeHTTP3
 	newConf.UseHTTP3Upstreams = dnsConf.UseHTTP3Upstreams
@@ -556,27 +441,19 @@ func startDNSServer() error {
 	Context.stats.Start()
 	Context.queryLog.Start()
 
-	const topClientsNumber = 100 // the number of clients to get
-	for _, ip := range Context.stats.TopClientsIP(topClientsNumber) {
-		Context.rdnsCh <- ip
-		Context.whoisCh <- ip
-	}
-
 	return nil
 }
 
 func reconfigureDNSServer() (err error) {
-	var newConf dnsforward.ServerConfig
-
 	tlsConf := &tlsConfigSettings{}
 	Context.tls.WriteDiskConfig(tlsConf)
 
-	newConf, err = generateServerConfig(tlsConf, httpRegister)
+	newConf, err := newServerConfig(tlsConf, httpRegister)
 	if err != nil {
 		return fmt.Errorf("generating forwarding dns server config: %w", err)
 	}
 
-	err = Context.dnsServer.Reconfigure(&newConf)
+	err = Context.dnsServer.Reconfigure(newConf)
 	if err != nil {
 		return fmt.Errorf("starting forwarding dns server: %w", err)
 	}
diff --git a/internal/home/home.go b/internal/home/home.go
index bdc0f86c..5355de2a 100644
--- a/internal/home/home.go
+++ b/internal/home/home.go
@@ -3,14 +3,12 @@ package home
 
 import (
 	"context"
-	"crypto/tls"
 	"crypto/x509"
 	"fmt"
 	"io/fs"
 	"net"
 	"net/http"
 	"net/netip"
-	"net/url"
 	"os"
 	"os/signal"
 	"path/filepath"
@@ -79,15 +77,8 @@ type homeContext struct {
 	pidFileName      string // PID file name.  Empty if no PID file was created.
 	controlLock      sync.Mutex
 	tlsRoots         *x509.CertPool // list of root CAs for TLSv1.2
-	client           *http.Client
 	appSignalChannel chan os.Signal // Channel for receiving OS signals by the console app
 
-	// rdnsCh is the channel for receiving IPs for rDNS processing.
-	rdnsCh chan netip.Addr
-
-	// whoisCh is the channel for receiving IPs for WHOIS processing.
-	whoisCh chan netip.Addr
-
 	// tlsCipherIDs are the ID of the cipher suites that AdGuard Home must use.
 	tlsCipherIDs []uint16
 
@@ -156,19 +147,6 @@ func setupContext(opts options) (err error) {
 	setupContextFlags(opts)
 
 	Context.tlsRoots = aghtls.SystemRootCAs()
-	Context.client = &http.Client{
-		Timeout: time.Minute * 5,
-		Transport: &http.Transport{
-			DialContext: customDialContext,
-			Proxy:       getHTTPProxy,
-			TLSClientConfig: &tls.Config{
-				RootCAs:      Context.tlsRoots,
-				CipherSuites: Context.tlsCipherIDs,
-				MinVersion:   tls.VersionTLS12,
-			},
-		},
-	}
-
 	Context.mux = http.NewServeMux()
 
 	if !Context.firstRun {
@@ -341,7 +319,7 @@ func initContextClients() (err error) {
 	}
 
 	Context.updater = updater.NewUpdater(&updater.Config{
-		Client:   Context.client,
+		Client:   config.DNS.DnsfilterConf.HTTPClient,
 		Version:  version.Version(),
 		Channel:  version.Channel(),
 		GOARCH:   runtime.GOARCH,
@@ -433,7 +411,7 @@ func setupDNSFilteringConf(conf *filtering.Config) (err error) {
 	conf.Filters = slices.Clone(config.Filters)
 	conf.WhitelistFilters = slices.Clone(config.WhitelistFilters)
 	conf.UserRules = slices.Clone(config.UserRules)
-	conf.HTTPClient = Context.client
+	conf.HTTPClient = httpClient()
 
 	cacheTime := time.Duration(conf.CacheTime) * time.Minute
 
@@ -634,10 +612,10 @@ func run(opts options, clientBuildFS fs.FS) {
 		Context.tls.start()
 
 		go func() {
-			sErr := startDNSServer()
-			if sErr != nil {
+			startErr := startDNSServer()
+			if startErr != nil {
 				closeDNSServer()
-				fatalOnError(sErr)
+				fatalOnError(startErr)
 			}
 		}()
 
@@ -996,62 +974,6 @@ func detectFirstRun() bool {
 	return errors.Is(err, os.ErrNotExist)
 }
 
-// Connect to a remote server resolving hostname using our own DNS server.
-//
-// TODO(e.burkov): This messy logic should be decomposed and clarified.
-//
-// TODO(a.garipov): Support network.
-func customDialContext(ctx context.Context, network, addr string) (conn net.Conn, err error) {
-	log.Debug("home: customdial: dialing addr %q for network %s", addr, network)
-
-	host, port, err := net.SplitHostPort(addr)
-	if err != nil {
-		return nil, err
-	}
-
-	dialer := &net.Dialer{
-		Timeout: time.Minute * 5,
-	}
-
-	if net.ParseIP(host) != nil || config.DNS.Port == 0 {
-		return dialer.DialContext(ctx, network, addr)
-	}
-
-	addrs, err := Context.dnsServer.Resolve(host)
-	if err != nil {
-		return nil, fmt.Errorf("resolving %q: %w", host, err)
-	}
-
-	log.Debug("dnsServer.Resolve: %q: %v", host, addrs)
-
-	if len(addrs) == 0 {
-		return nil, fmt.Errorf("couldn't lookup host: %q", host)
-	}
-
-	var dialErrs []error
-	for _, a := range addrs {
-		addr = net.JoinHostPort(a.String(), port)
-		conn, err = dialer.DialContext(ctx, network, addr)
-		if err != nil {
-			dialErrs = append(dialErrs, err)
-
-			continue
-		}
-
-		return conn, err
-	}
-
-	return nil, errors.List(fmt.Sprintf("couldn't dial to %s", addr), dialErrs...)
-}
-
-func getHTTPProxy(_ *http.Request) (*url.URL, error) {
-	if config.ProxyURL == "" {
-		return nil, nil
-	}
-
-	return url.Parse(config.ProxyURL)
-}
-
 // jsonError is a generic JSON error response.
 //
 // TODO(a.garipov): Merge together with the implementations in [dhcpd] and other
diff --git a/internal/home/httpclient.go b/internal/home/httpclient.go
new file mode 100644
index 00000000..ae41d6ac
--- /dev/null
+++ b/internal/home/httpclient.go
@@ -0,0 +1,47 @@
+package home
+
+import (
+	"context"
+	"crypto/tls"
+	"net"
+	"net/http"
+	"net/url"
+	"time"
+)
+
+// httpClient returns a new HTTP client that uses the AdGuard Home's own DNS
+// server for resolving hostnames.  The resulting client should not be used
+// until [Context.dnsServer] is initialized.
+//
+// TODO(a.garipov, e.burkov): This is rather messy.  Refactor.
+func httpClient() (c *http.Client) {
+	// Do not use Context.dnsServer.DialContext directly in the struct literal
+	// below, since Context.dnsServer may be nil when this function is called.
+	dialContext := func(ctx context.Context, network, addr string) (conn net.Conn, err error) {
+		return Context.dnsServer.DialContext(ctx, network, addr)
+	}
+
+	return &http.Client{
+		// TODO(a.garipov): Make configurable.
+		Timeout: time.Minute * 5,
+		Transport: &http.Transport{
+			DialContext: dialContext,
+			Proxy:       httpProxy,
+			TLSClientConfig: &tls.Config{
+				RootCAs:      Context.tlsRoots,
+				CipherSuites: Context.tlsCipherIDs,
+				MinVersion:   tls.VersionTLS12,
+			},
+		},
+	}
+}
+
+// httpProxy returns parses and returns an HTTP proxy URL from the config, if
+// any.
+func httpProxy(_ *http.Request) (u *url.URL, err error) {
+	if config.ProxyURL == "" {
+		return nil, nil
+	}
+
+	return url.Parse(config.ProxyURL)
+}