Improving Mac discovery

cmd/ctrld/cli.go

@@ -1138,6 +1138,7 @@ func validateConfig(cfg *ctrld.Config) {
 	os.Exit(1)
 }
 
+// NOTE: Add more case here once new validation tag is used in ctrld.Config struct.
 func fieldErrorMsg(fe validator.FieldError) string {
 	switch fe.Tag() {
 	case "oneof":
@@ -1165,6 +1166,8 @@ func fieldErrorMsg(fe validator.FieldError) string {
 		return fmt.Sprintf("must be one of: %q", strings.Join(ipStacks, " "))
 	case "iporempty":
 		return fmt.Sprintf("invalid IP format: %s", fe.Value())
+	case "file":
+		return fmt.Sprintf("filed does not exist: %s", fe.Value())
 	}
 	return ""
 }

cmd/ctrld/dns_proxy.go

@@ -55,7 +55,10 @@ func (p *prog) serveDNS(listenerNum string) error {
 		q := m.Question[0]
 		domain := canonicalName(q.Name)
 		reqId := requestID()
-		remoteAddr := spoofRemoteAddr(w.RemoteAddr(), p.mt.GetClientInfoByMac(macFromMsg(m)))
+		remoteIP, _, _ := net.SplitHostPort(w.RemoteAddr().String())
+		mac := macFromMsg(m)
+		ci := p.getClientInfo(remoteIP, mac)
+		remoteAddr := spoofRemoteAddr(w.RemoteAddr(), ci)
 		fmtSrcToDest := fmtRemoteToLocal(listenerNum, remoteAddr.String(), w.LocalAddr().String())
 		t := time.Now()
 		ctx := context.WithValue(context.Background(), ctrld.ReqIdCtxKey{}, reqId)
@@ -66,7 +69,7 @@ func (p *prog) serveDNS(listenerNum string) error {
 			answer = new(dns.Msg)
 			answer.SetRcode(m, dns.RcodeRefused)
 		} else {
-			answer = p.proxy(ctx, upstreams, failoverRcodes, m)
+			answer = p.proxy(ctx, upstreams, failoverRcodes, m, ci)
 			rtt := time.Since(t)
 			ctrld.Log(ctx, mainLog.Debug(), "received response of %d bytes in %s", answer.Len(), rtt)
 		}
@@ -202,7 +205,7 @@ networkRules:
 	return upstreams, matched
 }
 
-func (p *prog) proxy(ctx context.Context, upstreams []string, failoverRcodes []int, msg *dns.Msg) *dns.Msg {
+func (p *prog) proxy(ctx context.Context, upstreams []string, failoverRcodes []int, msg *dns.Msg, ci *ctrld.ClientInfo) *dns.Msg {
 	var staleAnswer *dns.Msg
 	serveStaleCache := p.cache != nil && p.cfg.Service.CacheServeStale
 	upstreamConfigs := p.upstreamConfigsFromUpstreamNumbers(upstreams)
@@ -245,12 +248,9 @@ func (p *prog) proxy(ctx context.Context, upstreams []string, failoverRcodes []i
 		return dnsResolver.Resolve(resolveCtx, msg)
 	}
 	resolve := func(n int, upstreamConfig *ctrld.UpstreamConfig, msg *dns.Msg) *dns.Msg {
-		if upstreamConfig.UpstreamSendClientInfo() {
+		if upstreamConfig.UpstreamSendClientInfo() && ci != nil {
-			ci := p.mt.GetClientInfoByMac(macFromMsg(msg))
+			ctrld.Log(ctx, mainLog.Debug(), "including client info with the request")
-			if ci != nil {
+			ctx = context.WithValue(ctx, ctrld.ClientInfoCtxKey{}, ci)
-				ctrld.Log(ctx, mainLog.Debug(), "including client info with the request")
-				ctx = context.WithValue(ctx, ctrld.ClientInfoCtxKey{}, ci)
-			}
 		}
 		answer, err := resolve1(n, upstreamConfig, msg)
 		if err != nil {
@@ -510,3 +510,16 @@ func inContainer() bool {
 	})
 	return ret
 }
+
+func (p *prog) getClientInfo(ip, mac string) *ctrld.ClientInfo {
+	ci := &ctrld.ClientInfo{}
+	if mac != "" {
+		ci.Mac = mac
+		ci.IP = p.ciTable.LookupIP(mac)
+	} else {
+		ci.IP = ip
+		ci.Mac = p.ciTable.LookupMac(ip)
+	}
+	ci.Hostname = p.ciTable.LookupHostname(ci.IP, ci.Mac)
+	return ci
+}

cmd/ctrld/dns_proxy_test.go

@@ -149,8 +149,8 @@ func TestCache(t *testing.T) {
 	answer2.SetRcode(msg, dns.RcodeRefused)
 	prog.cache.Add(dnscache.NewKey(msg, "upstream.0"), dnscache.NewValue(answer2, time.Now().Add(time.Minute)))
 
-	got1 := prog.proxy(context.Background(), []string{"upstream.1"}, nil, msg)
+	got1 := prog.proxy(context.Background(), []string{"upstream.1"}, nil, msg, nil)
-	got2 := prog.proxy(context.Background(), []string{"upstream.0"}, nil, msg)
+	got2 := prog.proxy(context.Background(), []string{"upstream.0"}, nil, msg, nil)
 	assert.NotSame(t, got1, got2)
 	assert.Equal(t, answer1.Rcode, got1.Rcode)
 	assert.Equal(t, answer2.Rcode, got2.Rcode)

cmd/ctrld/prog.go

@@ -48,11 +48,11 @@ type prog struct {
 	logConn net.Conn
 	cs      *controlServer
 
-	cfg    *ctrld.Config
+	cfg     *ctrld.Config
-	cache  dnscache.Cacher
+	cache   dnscache.Cacher
-	sema   semaphore
+	sema    semaphore
-	mt     *clientinfo.MacTable
+	ciTable *clientinfo.Table
-	router router.Router
+	router  router.Router
 
 	started   chan struct{}
 	onStarted []func()
@@ -106,24 +106,22 @@ func (p *prog) run() {
 		uc.Init()
 		if uc.BootstrapIP == "" {
 			uc.SetupBootstrapIP()
-			mainLog.Info().Msgf("Bootstrap IPs for upstream.%s: %q", n, uc.BootstrapIPs())
+			mainLog.Info().Msgf("bootstrap IPs for upstream.%s: %q", n, uc.BootstrapIPs())
 		} else {
-			mainLog.Info().Str("bootstrap_ip", uc.BootstrapIP).Msgf("Using bootstrap IP for upstream.%s", n)
+			mainLog.Info().Str("bootstrap_ip", uc.BootstrapIP).Msgf("using bootstrap IP for upstream.%s", n)
 		}
 		uc.SetCertPool(rootCertPool)
 		go uc.Ping()
 	}
 
-	p.mt = clientinfo.NewMacTable()
+	p.ciTable = clientinfo.NewTable(&cfg)
-	if p.cfg.HasUpstreamSendClientInfo() {
+	if leaseFile := p.cfg.Service.DHCPLeaseFile; leaseFile != "" {
-		mainLog.Debug().Msg("Sending client info enabled")
+		mainLog.Debug().Msgf("watching custom lease file: %s", leaseFile)
-		if err := p.mt.Init(); err == nil {
+		format := ctrld.LeaseFileFormat(p.cfg.Service.DHCPLeaseFileFormat)
-			mainLog.Debug().Msg("Start watching client info changes")
+		p.ciTable.AddLeaseFile(leaseFile, format)
-			go p.mt.WatchLeaseFiles()
-		} else {
-			mainLog.Warn().Err(err).Msg("could not record client info")
-		}
 	}
+	p.ciTable.Init()
+	go p.ciTable.RefreshLoop(p.stopCh)
 	go p.watchLinkState()
 
 	for listenerNum := range p.cfg.Listener {
@@ -136,7 +134,7 @@ func (p *prog) run() {
 				mainLog.Warn().Msgf("no default upstream for: [listener.%s]", listenerNum)
 			}
 			addr := net.JoinHostPort(listenerConfig.IP, strconv.Itoa(listenerConfig.Port))
-			mainLog.Info().Msgf("Starting DNS server on listener.%s: %s", listenerNum, addr)
+			mainLog.Info().Msgf("starting DNS server on listener.%s: %s", listenerNum, addr)
 			err := p.serveDNS(listenerNum)
 			if err != nil && !defaultConfigWritten && cdUID == "" {
 				mainLog.Fatal().Err(err).Msgf("Unable to start dns proxy on listener.%s", listenerNum)
@@ -162,7 +160,7 @@ func (p *prog) run() {
 					p.cfg.Service.AllocateIP = true
 					p.mu.Unlock()
 					p.preRun()
-					mainLog.Info().Msgf("Starting DNS server on listener.%s: %s", listenerNum, net.JoinHostPort(ip, strconv.Itoa(port)))
+					mainLog.Info().Msgf("starting DNS server on listener.%s: %s", listenerNum, net.JoinHostPort(ip, strconv.Itoa(port)))
 					if err := p.serveDNS(listenerNum); err != nil {
 						mainLog.Fatal().Err(err).Msgf("Unable to start dns proxy on listener.%s", listenerNum)
 						return

config.go

@@ -153,6 +153,12 @@ type ServiceConfig struct {
 	CacheTTLOverride      int    `mapstructure:"cache_ttl_override" toml:"cache_ttl_override,omitempty"`
 	CacheServeStale       bool   `mapstructure:"cache_serve_stale" toml:"cache_serve_stale,omitempty"`
 	MaxConcurrentRequests *int   `mapstructure:"max_concurrent_requests" toml:"max_concurrent_requests,omitempty" validate:"omitempty,gte=0"`
+	DHCPLeaseFile         string `mapstructure:"dhcp_lease_file_path" toml:"dhcp_lease_file_path" validate:"omitempty,file"`
+	DHCPLeaseFileFormat   string `mapstructure:"dhcp_lease_file_format" toml:"dhcp_lease_file_format" validate:"required_unless=DHCPLeaseFile '',omitempty,oneof=dnsmasq isc-dhcp"`
+	DiscoverMDNS          *bool  `mapstructure:"discover_mdns" toml:"discover_mdns,omitempty"`
+	DiscoverARP           *bool  `mapstructure:"discover_arp" toml:"discover_dhcp,omitempty"`
+	DiscoverDHCP          *bool  `mapstructure:"discover_dhcp" toml:"discover_dhcp,omitempty"`
+	DiscoverPtr           *bool  `mapstructure:"discover_ptr" toml:"discover_ptr,omitempty"`
 	Daemon                bool   `mapstructure:"-" toml:"-"`
 	AllocateIP            bool   `mapstructure:"-" toml:"-"`
 }
@@ -316,7 +322,7 @@ func (uc *UpstreamConfig) setupBootstrapIP(withBootstrapDNS bool) {
 			uc.bootstrapIPs4 = append(uc.bootstrapIPs4, ip)
 		}
 	}
-	ProxyLog.Debug().Msgf("Bootstrap IPs: %v", uc.bootstrapIPs)
+	ProxyLog.Debug().Msgf("bootstrap IPs: %v", uc.bootstrapIPs)
 }
 
 // ReBootstrap re-setup the bootstrap IP and the transport.

config_test.go

@@ -1,6 +1,7 @@
 package ctrld_test
 
 import (
+	"os"
 	"strings"
 	"testing"
 
@@ -91,6 +92,9 @@ func TestConfigValidation(t *testing.T) {
 		{"invalid rules", configWithInvalidRules(t), true},
 		{"invalid dns rcodes", configWithInvalidRcodes(t), true},
 		{"invalid max concurrent requests", configWithInvalidMaxConcurrentRequests(t), true},
+		{"non-existed lease file", configWithNonExistedLeaseFile(t), true},
+		{"lease file format required if lease file exist", configWithExistedLeaseFile(t), true},
+		{"invalid lease file format", configWithInvalidLeaseFileFormat(t), true},
 	}
 
 	for _, tc := range tests {
@@ -199,3 +203,25 @@ func configWithInvalidMaxConcurrentRequests(t *testing.T) *ctrld.Config {
 	cfg.Service.MaxConcurrentRequests = &n
 	return cfg
 }
+
+func configWithNonExistedLeaseFile(t *testing.T) *ctrld.Config {
+	cfg := defaultConfig(t)
+	cfg.Service.DHCPLeaseFile = "non-existed"
+	return cfg
+}
+
+func configWithExistedLeaseFile(t *testing.T) *ctrld.Config {
+	cfg := defaultConfig(t)
+	exe, err := os.Executable()
+	if err != nil {
+		t.Fatal(err)
+	}
+	cfg.Service.DHCPLeaseFile = exe
+	return cfg
+}
+
+func configWithInvalidLeaseFileFormat(t *testing.T) *ctrld.Config {
+	cfg := defaultConfig(t)
+	cfg.Service.DHCPLeaseFileFormat = "invalid"
+	return cfg
+}

internal/clientinfo/arp.go

@@ -0,0 +1,29 @@
+package clientinfo
+
+import "sync"
+
+type arpDiscover struct {
+	mac sync.Map // ip  => mac
+	ip  sync.Map // mac => ip
+}
+
+func (a *arpDiscover) refresh() error {
+	a.scan()
+	return nil
+}
+
+func (a *arpDiscover) LookupIP(mac string) string {
+	val, ok := a.ip.Load(mac)
+	if !ok {
+		return ""
+	}
+	return val.(string)
+}
+
+func (a *arpDiscover) LookupMac(ip string) string {
+	val, ok := a.mac.Load(ip)
+	if !ok {
+		return ""
+	}
+	return val.(string)
+}

internal/clientinfo/arp_linux.go

@@ -0,0 +1,28 @@
+package clientinfo
+
+import (
+	"bufio"
+	"os"
+	"strings"
+)
+
+const procNetArpFile = "/proc/net/arp"
+
+func (a *arpDiscover) scan() {
+	f, err := os.Open(procNetArpFile)
+	if err != nil {
+		return
+	}
+	defer f.Close()
+
+	s := bufio.NewScanner(f)
+	s.Scan() // skip header
+	for s.Scan() {
+		line := s.Text()
+		fields := strings.Fields(line)
+		ip := fields[0]
+		mac := fields[3]
+		a.mac.Store(ip, mac)
+		a.ip.Store(mac, ip)
+	}
+}

internal/clientinfo/arp_test.go

@@ -0,0 +1,23 @@
+package clientinfo
+
+import (
+	"sync"
+	"testing"
+)
+
+func TestArpScan(t *testing.T) {
+	a := &arpDiscover{}
+	a.scan()
+
+	for _, table := range []*sync.Map{&a.mac, &a.ip} {
+		count := 0
+		table.Range(func(key, value any) bool {
+			count++
+			t.Logf("%s => %s", key, value)
+			return true
+		})
+		if count == 0 {
+			t.Error("empty result from arp scan")
+		}
+	}
+}

internal/clientinfo/arp_unix.go

@@ -0,0 +1,30 @@
+//go:build !linux && !windows
+
+package clientinfo
+
+import (
+	"os/exec"
+	"strings"
+)
+
+func (a *arpDiscover) scan() {
+	data, err := exec.Command("arp", "-an").Output()
+	if err != nil {
+		return
+	}
+
+	for _, line := range strings.Split(string(data), "\n") {
+		fields := strings.Fields(line)
+		if len(fields) <= 3 {
+			continue
+		}
+
+		// trim brackets
+		ip := strings.ReplaceAll(fields[1], "(", "")
+		ip = strings.ReplaceAll(ip, ")", "")
+
+		mac := fields[3]
+		a.mac.Store(ip, mac)
+		a.ip.Store(mac, ip)
+	}
+}

internal/clientinfo/arp_windows.go

@@ -0,0 +1,38 @@
+package clientinfo
+
+import (
+	"os/exec"
+	"strings"
+)
+
+func (a *arpDiscover) scan() {
+	data, err := exec.Command("arp", "-a").Output()
+	if err != nil {
+		return
+	}
+
+	header := false
+	for _, line := range strings.Split(string(data), "\n") {
+		if len(line) == 0 {
+			continue // empty lines
+		}
+		if line[0] != ' ' {
+			header = true // "Interface:" lines, next is header line.
+			continue
+		}
+		if header {
+			header = false // header lines
+			continue
+		}
+
+		fields := strings.Fields(line)
+		if len(fields) < 2 {
+			continue
+		}
+
+		ip := fields[0]
+		mac := strings.ReplaceAll(fields[1], "-", ":")
+		a.mac.Store(ip, mac)
+		a.ip.Store(mac, ip)
+	}
+}

internal/clientinfo/client_info.go

@@ -1,211 +1,194 @@
 package clientinfo
 
 import (
-	"bufio"
-	"bytes"
-	"fmt"
-	"io"
-	"log"
-	"net"
-	"os"
 	"strings"
-	"sync"
 	"time"
 
-	"github.com/fsnotify/fsnotify"
-	"tailscale.com/util/lineread"
-
 	"github.com/Control-D-Inc/ctrld"
 )
 
-// clientInfoFiles specifies client info files and how to read them on supported platforms.
+// IpResolver is the interface for retrieving IP from Mac.
-var clientInfoFiles = map[string]ctrld.LeaseFileFormat{
+type IpResolver interface {
-	"/tmp/dnsmasq.leases":                      ctrld.Dnsmasq,  // ddwrt
+	LookupIP(mac string) string
-	"/tmp/dhcp.leases":                         ctrld.Dnsmasq,  // openwrt
-	"/var/lib/misc/dnsmasq.leases":             ctrld.Dnsmasq,  // merlin
-	"/mnt/data/udapi-config/dnsmasq.lease":     ctrld.Dnsmasq,  // UDM Pro
-	"/data/udapi-config/dnsmasq.lease":         ctrld.Dnsmasq,  // UDR
-	"/etc/dhcpd/dhcpd-leases.log":              ctrld.Dnsmasq,  // Synology
-	"/tmp/var/lib/misc/dnsmasq.leases":         ctrld.Dnsmasq,  // Tomato
-	"/run/dnsmasq-dhcp.leases":                 ctrld.Dnsmasq,  // EdgeOS
-	"/run/dhcpd.leases":                        ctrld.IscDhcpd, // EdgeOS
-	"/var/dhcpd/var/db/dhcpd.leases":           ctrld.IscDhcpd, // Pfsense
-	"/home/pi/.router/run/dhcp/dnsmasq.leases": ctrld.Dnsmasq,  // Firewalla
 }
 
-// NewMacTable returns new Mac table to record client information.
+// MacResolver is the interface for retrieving Mac from IP.
-func NewMacTable() *MacTable {
+type MacResolver interface {
-	return &MacTable{}
+	LookupMac(ip string) string
 }
 
-// MacTable records clients information by MAC address.
+// HostnameByIpResolver is the interface for retrieving hostname from IP.
-type MacTable struct {
+type HostnameByIpResolver interface {
-	mac     sync.Map
+	LookupHostnameByIP(ip string) string
-	watcher *fsnotify.Watcher
 }
 
-// Init initializes recording client info.
+// HostnameByMacResolver is the interface for retrieving hostname from Mac.
-func (mt *MacTable) Init() error {
+type HostnameByMacResolver interface {
-	watcher, err := fsnotify.NewWatcher()
+	LookupHostnameByMac(mac string) string
-	if err != nil {
-		return err
-	}
-	mt.watcher = watcher
-	for file, format := range clientInfoFiles {
-		// Ignore errors for default lease files.
-		_ = mt.AddLeaseFile(file, format)
-	}
-	return nil
 }
 
-// AddLeaseFile adds given lease file for reading/watching clients info.
+type HostnameResolver interface {
-func (mt *MacTable) AddLeaseFile(name string, format ctrld.LeaseFileFormat) error {
+	HostnameByIpResolver
-	if err := mt.readLeaseFile(name, format); err != nil {
+	HostnameByMacResolver
-		return fmt.Errorf("could not read lease file: %w", err)
-	}
-	clientInfoFiles[name] = format
-	return mt.watcher.Add(name)
 }
 
-// GetClientInfoByMac returns ClientInfo for the client associated with the given MAC address.
+type refresher interface {
-func (mt *MacTable) GetClientInfoByMac(mac string) *ctrld.ClientInfo {
+	refresh() error
-	if mac == "" {
-		return nil
-	}
-	val, ok := mt.mac.Load(mac)
-	if !ok {
-		return nil
-	}
-	return val.(*ctrld.ClientInfo)
 }
 
-// WatchLeaseFiles watches changes happens in dnsmasq/dhcpd
+type Table struct {
-// lease files, perform updating to mac table if necessary.
+	ipResolvers       []IpResolver
-func (mt *MacTable) WatchLeaseFiles() {
+	macResolvers      []MacResolver
-	if mt.watcher == nil {
+	hostnameResolvers []HostnameResolver
+	refreshers        []refresher
+
+	dhcp   *dhcp
+	merlin *merlinDiscover
+	arp    *arpDiscover
+	ptr    *ptrDiscover
+	mdns   *mdns
+	cfg    *ctrld.Config
+}
+
+func NewTable(cfg *ctrld.Config) *Table {
+	return &Table{cfg: cfg}
+}
+
+func (t *Table) AddLeaseFile(name string, format ctrld.LeaseFileFormat) {
+	if !t.discoverDHCP() {
 		return
 	}
+	clientInfoFiles[name] = format
+}
+
+func (t *Table) RefreshLoop(stopCh chan struct{}) {
 	timer := time.NewTicker(time.Minute * 5)
 	for {
 		select {
 		case <-timer.C:
-			for _, name := range mt.watcher.WatchList() {
+			for _, r := range t.refreshers {
-				format := clientInfoFiles[name]
+				_ = r.refresh()
-				if err := mt.readLeaseFile(name, format); err != nil {
-					ctrld.ProxyLog.Err(err).Str("file", name).Msg("failed to update lease file")
-				}
 			}
-		case event, ok := <-mt.watcher.Events:
+		case <-stopCh:
-			if !ok {
+			return
-				return
-			}
-			if event.Has(fsnotify.Write) {
-				format := clientInfoFiles[event.Name]
-				if err := mt.readLeaseFile(event.Name, format); err != nil && !os.IsNotExist(err) {
-					ctrld.ProxyLog.Err(err).Str("file", event.Name).Msg("leases file changed but failed to update client info")
-				}
-			}
-		case err, ok := <-mt.watcher.Errors:
-			if !ok {
-				return
-			}
-			ctrld.ProxyLog.Err(err).Msg("could not watch client info file")
 		}
 	}
 }
 
-// readLeaseFile reads the lease file with given format, saving client information to mac table.
+func (t *Table) Init() {
-func (mt *MacTable) readLeaseFile(name string, format ctrld.LeaseFileFormat) error {
+	if t.discoverDHCP() || t.discoverARP() {
-	switch format {
+		t.merlin = &merlinDiscover{}
-	case ctrld.Dnsmasq:
+		if err := t.merlin.refresh(); err != nil {
-		return mt.dnsmasqReadClientInfoFile(name)
+			ctrld.ProxyLog.Error().Err(err).Msg("could not init Merlin discover")
-	case ctrld.IscDhcpd:
+		} else {
-		return mt.iscDHCPReadClientInfoFile(name)
+			t.hostnameResolvers = append(t.hostnameResolvers, t.merlin)
+			t.refreshers = append(t.refreshers, t.merlin)
+		}
+	}
+	if t.discoverDHCP() {
+		t.dhcp = &dhcp{}
+		ctrld.ProxyLog.Debug().Msg("start dhcp discovery")
+		if err := t.dhcp.refresh(); err != nil {
+			ctrld.ProxyLog.Error().Err(err).Msg("could not init DHCP discover")
+		} else {
+			t.ipResolvers = append(t.ipResolvers, t.dhcp)
+			t.macResolvers = append(t.macResolvers, t.dhcp)
+			t.hostnameResolvers = append(t.hostnameResolvers, t.dhcp)
+			t.refreshers = append(t.refreshers, t.dhcp)
+		}
+		go t.dhcp.watchChanges()
+	}
+	if t.discoverARP() {
+		t.arp = &arpDiscover{}
+		ctrld.ProxyLog.Debug().Msg("start arp discovery")
+		if err := t.arp.refresh(); err != nil {
+			ctrld.ProxyLog.Error().Err(err).Msg("could not init ARP discover")
+		} else {
+			t.ipResolvers = append(t.ipResolvers, t.arp)
+			t.macResolvers = append(t.macResolvers, t.arp)
+			t.refreshers = append(t.refreshers, t.arp)
+		}
+	}
+	if t.discoverPTR() {
+		t.ptr = &ptrDiscover{resolver: ctrld.NewPrivateResolver()}
+		ctrld.ProxyLog.Debug().Msg("start ptr discovery")
+		if err := t.ptr.refresh(); err != nil {
+			ctrld.ProxyLog.Error().Err(err).Msg("could not init PTR discover")
+		} else {
+			t.hostnameResolvers = append(t.hostnameResolvers, t.ptr)
+			t.refreshers = append(t.refreshers, t.ptr)
+		}
+	}
+	if t.discoverMDNS() {
+		t.mdns = &mdns{}
+		ctrld.ProxyLog.Debug().Msg("start mdns discovery")
+		if err := t.mdns.init(); err != nil {
+			ctrld.ProxyLog.Error().Err(err).Msg("could not init mDNS discover")
+		} else {
+			t.hostnameResolvers = append(t.hostnameResolvers, t.mdns)
+		}
 	}
-	return fmt.Errorf("unsupported format: %s, file: %s", format, name)
 }
 
-// dnsmasqReadClientInfoFile populates mac table with client info reading from dnsmasq lease file.
+func (t *Table) LookupIP(mac string) string {
-func (mt *MacTable) dnsmasqReadClientInfoFile(name string) error {
+	for _, r := range t.ipResolvers {
-	f, err := os.Open(name)
+		if ip := r.LookupIP(mac); ip != "" {
-	if err != nil {
+			return ip
-		return err
+		}
 	}
-	defer f.Close()
+	return ""
-	return mt.dnsmasqReadClientInfoReader(f)
-
 }
 
-// dnsmasqReadClientInfoReader likes ctrld.Dnsmasq, but reading from an io.Reader instead of file.
+func (t *Table) LookupMac(ip string) string {
-func (mt *MacTable) dnsmasqReadClientInfoReader(reader io.Reader) error {
+	t.arp.mac.Range(func(key, value any) bool {
-	return lineread.Reader(reader, func(line []byte) error {
+		return true
-		fields := bytes.Fields(line)
-		if len(fields) < 4 {
-			return nil
-		}
-		mac := string(fields[1])
-		if _, err := net.ParseMAC(mac); err != nil {
-			// The second field is not a mac, skip.
-			return nil
-		}
-		ip := normalizeIP(string(fields[2]))
-		if net.ParseIP(ip) == nil {
-			log.Printf("invalid ip address entry: %q", ip)
-			ip = ""
-		}
-		hostname := string(fields[3])
-		mt.mac.Store(mac, &ctrld.ClientInfo{Mac: mac, IP: ip, Hostname: hostname})
-		return nil
 	})
-}
+	for _, r := range t.macResolvers {
-
+		if mac := r.LookupMac(ip); mac != "" {
-// iscDHCPReadClientInfoFile populates mac table with client info reading from isc-dhcpd lease file.
+			return mac
-func (mt *MacTable) iscDHCPReadClientInfoFile(name string) error {
-	f, err := os.Open(name)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-	return mt.iscDHCPReadClientInfoReader(f)
-}
-
-// iscDHCPReadClientInfoReader likes ctrld.IscDhcpd, but reading from an io.Reader instead of file.
-func (mt *MacTable) iscDHCPReadClientInfoReader(reader io.Reader) error {
-	s := bufio.NewScanner(reader)
-	var ip, mac, hostname string
-	for s.Scan() {
-		line := s.Text()
-		if strings.HasPrefix(line, "}") {
-			if mac != "" {
-				mt.mac.Store(mac, &ctrld.ClientInfo{Mac: mac, IP: ip, Hostname: hostname})
-				ip, mac, hostname = "", "", ""
-			}
-			continue
-		}
-		fields := strings.Fields(line)
-		if len(fields) < 2 {
-			continue
-		}
-		switch fields[0] {
-		case "lease":
-			ip = normalizeIP(strings.ToLower(fields[1]))
-			if net.ParseIP(ip) == nil {
-				log.Printf("invalid ip address entry: %q", ip)
-				ip = ""
-			}
-		case "hardware":
-			if len(fields) >= 3 {
-				mac = strings.ToLower(strings.TrimRight(fields[2], ";"))
-				if _, err := net.ParseMAC(mac); err != nil {
-					// Invalid mac, skip.
-					mac = ""
-				}
-			}
-		case "client-hostname":
-			hostname = strings.Trim(fields[1], `";`)
 		}
 	}
-	return nil
+	return ""
+}
+
+func (t *Table) LookupHostname(ip, mac string) string {
+	for _, r := range t.hostnameResolvers {
+		if name := r.LookupHostnameByIP(ip); name != "" {
+			return name
+		}
+		if name := r.LookupHostnameByMac(mac); name != "" {
+			return name
+		}
+	}
+	return ""
+}
+
+func (t *Table) discoverDHCP() bool {
+	if t.cfg.Service.DiscoverDHCP == nil {
+		return true
+	}
+	return *t.cfg.Service.DiscoverDHCP
+}
+
+func (t *Table) discoverARP() bool {
+	if t.cfg.Service.DiscoverARP == nil {
+		return true
+	}
+	return *t.cfg.Service.DiscoverARP
+}
+
+func (t *Table) discoverMDNS() bool {
+	if t.cfg.Service.DiscoverMDNS == nil {
+		return true
+	}
+	return *t.cfg.Service.DiscoverMDNS
+}
+
+func (t *Table) discoverPTR() bool {
+	if t.cfg.Service.DiscoverPtr == nil {
+		return true
+	}
+	return *t.cfg.Service.DiscoverPtr
 }
 
 // normalizeIP normalizes the ip parsed from dnsmasq/dhcpd lease file.
@@ -217,3 +200,10 @@ func normalizeIP(in string) string {
 	}
 	return in
 }
+
+func normalizeHostname(name string) string {
+	if before, _, found := strings.Cut(name, "."); found {
+		return before // remove ".local.", ".lan.", ... suffix
+	}
+	return strings.ToLower(name)
+}

internal/clientinfo/client_info_test.go

@@ -1,11 +1,7 @@
 package clientinfo
 
 import (
-	"io"
-	"strings"
 	"testing"
-
-	"github.com/Control-D-Inc/ctrld"
 )
 
 func Test_normalizeIP(t *testing.T) {
@@ -29,79 +25,3 @@ func Test_normalizeIP(t *testing.T) {
 		})
 	}
 }
-
-func Test_readClientInfoReader(t *testing.T) {
-	mt := NewMacTable()
-	tests := []struct {
-		name     string
-		in       string
-		readFunc func(r io.Reader) error
-		mac      string
-	}{
-		{
-			"good dnsmasq",
-			`1683329857 e6:20:59:b8:c1:6d 192.168.1.186 * 01:e6:20:59:b8:c1:6d
-`,
-			mt.dnsmasqReadClientInfoReader,
-			"e6:20:59:b8:c1:6d",
-		},
-		{
-			"bad dnsmasq seen on UDMdream machine",
-			`1683329857 e6:20:59:b8:c1:6e 192.168.1.111 * 01:e6:20:59:b8:c1:6e
-duid 00:01:00:01:2b:e4:2e:2c:52:52:14:26:dc:1c
-1683322985 117442354 2600:4040:b0e6:b700::111 ASDASD 00:01:00:01:2a:d0:b9:81:00:07:32:4c:1c:07
-`,
-			mt.dnsmasqReadClientInfoReader,
-			"e6:20:59:b8:c1:6e",
-		},
-		{
-			"isc-dhcpd good",
-			`lease 192.168.1.1 {
-    hardware ethernet 00:00:00:00:00:01;
-    client-hostname "host-1";
-}
-`,
-			mt.iscDHCPReadClientInfoReader,
-			"00:00:00:00:00:01",
-		},
-		{
-			"isc-dhcpd bad mac",
-			`lease 192.168.1.1 {
-    hardware ethernet invalid-mac;
-    client-hostname "host-1";
-}
-
-lease 192.168.1.2 {
-    hardware ethernet 00:00:00:00:00:02;
-    client-hostname "host-2";
-}
-`,
-			mt.iscDHCPReadClientInfoReader,
-			"00:00:00:00:00:02",
-		},
-		{
-			"",
-			`1685794060 00:00:00:00:00:04 192.168.0.209 cuonglm-ThinkPad-X1-Carbon-Gen-9 00:00:00:00:00:04 9`,
-			mt.dnsmasqReadClientInfoReader,
-			"00:00:00:00:00:04",
-		},
-	}
-
-	for _, tc := range tests {
-		t.Run(tc.name, func(t *testing.T) {
-			mt.mac.Delete(tc.mac)
-			if err := tc.readFunc(strings.NewReader(tc.in)); err != nil {
-				t.Errorf("readClientInfoReader() error = %v", err)
-			}
-			info, existed := mt.mac.Load(tc.mac)
-			if !existed {
-				t.Error("client info missing")
-			}
-			if ci, ok := info.(*ctrld.ClientInfo); ok && existed && ci.Mac != tc.mac {
-				t.Errorf("mac mismatched, got: %q, want: %q", ci.Mac, tc.mac)
-			} else {
-				t.Log(ci)
-			}
-		})
-	}
-}

internal/clientinfo/dhcp.go

@@ -0,0 +1,256 @@
+package clientinfo
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"net"
+	"net/netip"
+	"os"
+	"strings"
+	"sync"
+
+	"github.com/Control-D-Inc/ctrld"
+	"tailscale.com/net/interfaces"
+	"tailscale.com/util/lineread"
+
+	"github.com/fsnotify/fsnotify"
+)
+
+type dhcp struct {
+	mac2name sync.Map // mac => name
+	ip2name  sync.Map // ip  => name
+	ip       sync.Map // mac => ip
+	mac      sync.Map // ip  => mac
+
+	watcher *fsnotify.Watcher
+}
+
+func (d *dhcp) refresh() error {
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		return err
+	}
+	d.addSelf()
+	d.watcher = watcher
+	for file, format := range clientInfoFiles {
+		// Ignore errors for default lease files.
+		_ = d.addLeaseFile(file, format)
+	}
+	return nil
+}
+
+func (d *dhcp) watchChanges() {
+	if d.watcher == nil {
+		return
+	}
+	for {
+		select {
+		case event, ok := <-d.watcher.Events:
+			if !ok {
+				return
+			}
+			if event.Has(fsnotify.Write) {
+				format := clientInfoFiles[event.Name]
+				if err := d.readLeaseFile(event.Name, format); err != nil && !os.IsNotExist(err) {
+					ctrld.ProxyLog.Err(err).Str("file", event.Name).Msg("leases file changed but failed to update client info")
+				}
+			}
+		case err, ok := <-d.watcher.Errors:
+			if !ok {
+				return
+			}
+			ctrld.ProxyLog.Err(err).Msg("could not watch client info file")
+		}
+	}
+
+}
+
+func (d *dhcp) LookupIP(mac string) string {
+	val, ok := d.ip.Load(mac)
+	if !ok {
+		return ""
+	}
+	return val.(string)
+}
+
+func (d *dhcp) LookupMac(ip string) string {
+	val, ok := d.mac.Load(ip)
+	if !ok {
+		return ""
+	}
+	return val.(string)
+}
+
+func (d *dhcp) LookupHostnameByIP(ip string) string {
+	val, ok := d.ip2name.Load(ip)
+	if !ok {
+		return ""
+	}
+	return val.(string)
+}
+
+func (d *dhcp) LookupHostnameByMac(mac string) string {
+	val, ok := d.mac2name.Load(mac)
+	if !ok {
+		return ""
+	}
+	return val.(string)
+}
+
+// AddLeaseFile adds given lease file for reading/watching clients info.
+func (d *dhcp) addLeaseFile(name string, format ctrld.LeaseFileFormat) error {
+	if d.watcher == nil {
+		return nil
+	}
+	if err := d.readLeaseFile(name, format); err != nil {
+		return fmt.Errorf("could not read lease file: %w", err)
+	}
+	clientInfoFiles[name] = format
+	return d.watcher.Add(name)
+}
+
+// readLeaseFile reads the lease file with given format, saving client information to dhcp table.
+func (d *dhcp) readLeaseFile(name string, format ctrld.LeaseFileFormat) error {
+	switch format {
+	case ctrld.Dnsmasq:
+		return d.dnsmasqReadClientInfoFile(name)
+	case ctrld.IscDhcpd:
+		return d.iscDHCPReadClientInfoFile(name)
+	}
+	return fmt.Errorf("unsupported format: %s, file: %s", format, name)
+}
+
+// dnsmasqReadClientInfoFile populates dhcp table with client info reading from dnsmasq lease file.
+func (d *dhcp) dnsmasqReadClientInfoFile(name string) error {
+	f, err := os.Open(name)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	return d.dnsmasqReadClientInfoReader(f)
+
+}
+
+// dnsmasqReadClientInfoReader likes ctrld.Dnsmasq, but reading from an io.Reader instead of file.
+func (d *dhcp) dnsmasqReadClientInfoReader(reader io.Reader) error {
+	return lineread.Reader(reader, func(line []byte) error {
+		fields := bytes.Fields(line)
+		if len(fields) < 4 {
+			return nil
+		}
+
+		mac := string(fields[1])
+		if _, err := net.ParseMAC(mac); err != nil {
+			// The second field is not a dhcp, skip.
+			return nil
+		}
+		ip := normalizeIP(string(fields[2]))
+		if net.ParseIP(ip) == nil {
+			ctrld.ProxyLog.Warn().Msgf("invalid ip address entry: %q", ip)
+			ip = ""
+		}
+
+		d.mac.Store(ip, mac)
+		d.ip.Store(mac, ip)
+		hostname := string(fields[3])
+		if hostname == "*" {
+			return nil
+		}
+		name := normalizeHostname(hostname)
+		d.mac2name.Store(mac, name)
+		d.ip2name.Store(ip, name)
+		return nil
+	})
+}
+
+// iscDHCPReadClientInfoFile populates dhcp table with client info reading from isc-dhcpd lease file.
+func (d *dhcp) iscDHCPReadClientInfoFile(name string) error {
+	f, err := os.Open(name)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	return d.iscDHCPReadClientInfoReader(f)
+}
+
+// iscDHCPReadClientInfoReader likes ctrld.IscDhcpd, but reading from an io.Reader instead of file.
+func (d *dhcp) iscDHCPReadClientInfoReader(reader io.Reader) error {
+	s := bufio.NewScanner(reader)
+	var ip, mac, hostname string
+	for s.Scan() {
+		line := s.Text()
+		if strings.HasPrefix(line, "}") {
+			d.mac.Store(ip, mac)
+			d.ip.Store(mac, ip)
+			if hostname != "" && hostname != "*" {
+				name := normalizeHostname(hostname)
+				d.mac2name.Store(mac, name)
+				d.ip2name.Store(ip, hostname)
+				ip, mac, hostname = "", "", ""
+			}
+			continue
+		}
+		fields := strings.Fields(line)
+		if len(fields) < 2 {
+			continue
+		}
+		switch fields[0] {
+		case "lease":
+			ip = normalizeIP(strings.ToLower(fields[1]))
+			if net.ParseIP(ip) == nil {
+				ctrld.ProxyLog.Warn().Msgf("invalid ip address entry: %q", ip)
+				ip = ""
+			}
+		case "hardware":
+			if len(fields) >= 3 {
+				mac = strings.ToLower(strings.TrimRight(fields[2], ";"))
+				if _, err := net.ParseMAC(mac); err != nil {
+					// Invalid dhcp, skip.
+					mac = ""
+				}
+			}
+		case "client-hostname":
+			hostname = strings.Trim(fields[1], `";`)
+		}
+	}
+	return nil
+}
+
+// addSelf populates current host info to dhcp, so queries from
+// the host itself can be attached with proper client info.
+func (d *dhcp) addSelf() {
+	hostname, err := os.Hostname()
+	if err != nil {
+		ctrld.ProxyLog.Err(err).Msg("could not get hostname")
+		return
+	}
+	hostname = normalizeHostname(hostname)
+	d.ip2name.Store("127.0.0.1", hostname)
+	d.ip2name.Store("::1", hostname)
+	interfaces.ForeachInterface(func(i interfaces.Interface, prefixes []netip.Prefix) {
+		mac := i.HardwareAddr.String()
+		// Skip loopback interfaces, info was stored above.
+		if mac == "" {
+			return
+		}
+		addrs, _ := i.Addrs()
+		for _, addr := range addrs {
+			ipNet, ok := addr.(*net.IPNet)
+			if !ok {
+				continue
+			}
+			ip := ipNet.IP
+			d.mac.Store(ip.String(), mac)
+			d.ip.Store(mac, ip.String())
+			if ip.To4() != nil {
+				d.mac.Store("127.0.0.1", mac)
+			} else {
+				d.mac.Store("::1", mac)
+			}
+			d.mac2name.Store(mac, hostname)
+			d.ip2name.Store(ip.String(), hostname)
+		}
+	})
+}

internal/clientinfo/dhcp_lease_files.go

@@ -0,0 +1,18 @@
+package clientinfo
+
+import "github.com/Control-D-Inc/ctrld"
+
+// clientInfoFiles specifies client info files and how to read them on supported platforms.
+var clientInfoFiles = map[string]ctrld.LeaseFileFormat{
+	"/tmp/dnsmasq.leases":                      ctrld.Dnsmasq,  // ddwrt
+	"/tmp/dhcp.leases":                         ctrld.Dnsmasq,  // openwrt
+	"/var/lib/misc/dnsmasq.leases":             ctrld.Dnsmasq,  // merlin
+	"/mnt/data/udapi-config/dnsmasq.lease":     ctrld.Dnsmasq,  // UDM Pro
+	"/data/udapi-config/dnsmasq.lease":         ctrld.Dnsmasq,  // UDR
+	"/etc/dhcpd/dhcpd-leases.log":              ctrld.Dnsmasq,  // Synology
+	"/tmp/var/lib/misc/dnsmasq.leases":         ctrld.Dnsmasq,  // Tomato
+	"/run/dnsmasq-dhcp.leases":                 ctrld.Dnsmasq,  // EdgeOS
+	"/run/dhcpd.leases":                        ctrld.IscDhcpd, // EdgeOS
+	"/var/dhcpd/var/db/dhcpd.leases":           ctrld.IscDhcpd, // Pfsense
+	"/home/pi/.router/run/dhcp/dnsmasq.leases": ctrld.Dnsmasq,  // Firewalla
+}

internal/clientinfo/dhcp_test.go

@@ -0,0 +1,88 @@
+package clientinfo
+
+import (
+	"io"
+	"strings"
+	"testing"
+)
+
+func Test_readClientInfoReader(t *testing.T) {
+	d := &dhcp{}
+	tests := []struct {
+		name     string
+		in       string
+		readFunc func(r io.Reader) error
+		mac      string
+		hostname string
+	}{
+		{
+			"good dnsmasq",
+			`1683329857 e6:20:59:b8:c1:6d 192.168.1.186 host1 01:e6:20:59:b8:c1:6d
+`,
+			d.dnsmasqReadClientInfoReader,
+			"e6:20:59:b8:c1:6d",
+			"host1",
+		},
+		{
+			"bad dnsmasq seen on UDMdream machine",
+			`1683329857 e6:20:59:b8:c1:6e 192.168.1.111 host1 01:e6:20:59:b8:c1:6e
+duid 00:01:00:01:2b:e4:2e:2c:52:52:14:26:dc:1c
+1683322985 117442354 2600:4040:b0e6:b700::111 ASDASD 00:01:00:01:2a:d0:b9:81:00:07:32:4c:1c:07
+`,
+			d.dnsmasqReadClientInfoReader,
+			"e6:20:59:b8:c1:6e",
+			"host1",
+		},
+		{
+			"isc-dhcpd good",
+			`lease 192.168.1.1 {
+    hardware ethernet 00:00:00:00:00:01;
+    client-hostname "host-1";
+}
+`,
+			d.iscDHCPReadClientInfoReader,
+			"00:00:00:00:00:01",
+			"host-1",
+		},
+		{
+			"isc-dhcpd bad dhcp",
+			`lease 192.168.1.1 {
+    hardware ethernet invalid-dhcp;
+    client-hostname "host-1";
+}
+
+lease 192.168.1.2 {
+    hardware ethernet 00:00:00:00:00:02;
+    client-hostname "host-2";
+}
+`,
+			d.iscDHCPReadClientInfoReader,
+			"00:00:00:00:00:02",
+			"host-2",
+		},
+		{
+			"",
+			`1685794060 00:00:00:00:00:04 192.168.0.209 example 00:00:00:00:00:04 9`,
+			d.dnsmasqReadClientInfoReader,
+			"00:00:00:00:00:04",
+			"example",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			d.mac2name.Delete(tc.mac)
+			if err := tc.readFunc(strings.NewReader(tc.in)); err != nil {
+				t.Errorf("readClientInfoReader() error = %v", err)
+			}
+			val, existed := d.mac2name.Load(tc.mac)
+			if !existed {
+				t.Error("client info missing")
+			}
+			hostname := val.(string)
+			if existed && hostname != tc.hostname {
+				t.Errorf("hostname mismatched, want: %q, got: %q", tc.hostname, hostname)
+			}
+		})
+	}
+}

internal/clientinfo/mdns.go

@@ -0,0 +1,163 @@
+package clientinfo
+
+import (
+	"context"
+	"errors"
+	"net"
+	"sync"
+	"time"
+
+	"github.com/miekg/dns"
+	"tailscale.com/logtail/backoff"
+
+	"github.com/Control-D-Inc/ctrld"
+	ctrldnet "github.com/Control-D-Inc/ctrld/internal/net"
+)
+
+var (
+	mdnsV4Addr = &net.UDPAddr{
+		IP:   net.ParseIP("224.0.0.251"),
+		Port: 5353,
+	}
+	mdnsV6Addr = &net.UDPAddr{
+		IP:   net.ParseIP("ff02::fb"),
+		Port: 5353,
+	}
+)
+
+type mdns struct {
+	name sync.Map // ip => hostname
+}
+
+func (m *mdns) LookupHostnameByIP(ip string) string {
+	val, ok := m.name.Load(ip)
+	if !ok {
+		return ""
+	}
+	return val.(string)
+}
+
+func (m *mdns) LookupHostnameByMac(mac string) string {
+	return ""
+}
+
+func (m *mdns) init() error {
+	ifaces, err := multicastInterfaces()
+	if err != nil {
+		return err
+	}
+
+	v4ConnList := make([]*net.UDPConn, 0, len(ifaces))
+	v6ConnList := make([]*net.UDPConn, 0, len(ifaces))
+	for _, iface := range ifaces {
+		if iface.Flags&net.FlagLoopback != 0 {
+			continue
+		}
+		if conn, err := net.ListenMulticastUDP("udp4", &iface, mdnsV4Addr); err == nil {
+			v4ConnList = append(v4ConnList, conn)
+			go m.readLoop(conn)
+		}
+		if ctrldnet.IPv6Available(context.Background()) {
+			if conn, err := net.ListenMulticastUDP("udp6", &iface, mdnsV6Addr); err == nil {
+				v6ConnList = append(v6ConnList, conn)
+				go m.readLoop(conn)
+			}
+		}
+	}
+
+	go func() {
+		bo := backoff.NewBackoff("mdns probe", func(format string, args ...any) {}, time.Second*30)
+		for {
+			err := m.probe(v4ConnList, v6ConnList)
+			if err != nil {
+				ctrld.ProxyLog.Warn().Err(err).Msg("error while probing mdns")
+			}
+			bo.BackOff(context.Background(), errors.New("mdns probe backoff"))
+		}
+	}()
+
+	return nil
+}
+
+func (m *mdns) readLoop(conn *net.UDPConn) {
+	defer conn.Close()
+	buf := make([]byte, dns.MaxMsgSize)
+
+	for {
+		_ = conn.SetReadDeadline(time.Now().Add(time.Second * 30))
+		n, _, err := conn.ReadFromUDP(buf)
+		if err != nil {
+			if err, ok := err.(*net.OpError); ok {
+				if err.Timeout() || err.Temporary() {
+					continue
+				}
+				ctrld.ProxyLog.Debug().Err(err).Msg("mdns readLoop error")
+			}
+			return
+		}
+
+		var msg dns.Msg
+		if err := msg.Unpack(buf[:n]); err != nil {
+			continue
+		}
+
+		var ip, name string
+		for _, answer := range msg.Answer {
+			switch ar := answer.(type) {
+			case *dns.A:
+				ip, name = ar.A.String(), ar.Hdr.Name
+			case *dns.AAAA:
+				ip, name = ar.AAAA.String(), ar.Hdr.Name
+			}
+			if ip != "" && name != "" {
+				name = normalizeHostname(name)
+				ctrld.ProxyLog.Debug().Msgf("Found hostname: %q, ip: %q via mdns", name, ip)
+				m.name.Store(ip, name)
+			}
+		}
+	}
+}
+
+func (m *mdns) probe(v4connList, v6connList []*net.UDPConn) error {
+	msg := new(dns.Msg)
+	msg.Question = make([]dns.Question, len(services))
+	for i, service := range services {
+		msg.Question[i] = dns.Question{
+			Name:   dns.CanonicalName(service),
+			Qtype:  dns.TypePTR,
+			Qclass: dns.ClassINET,
+		}
+	}
+
+	buf, err := msg.Pack()
+	if err != nil {
+		return err
+	}
+	do := func(connList []*net.UDPConn, remoteAddr net.Addr) error {
+		for _, conn := range connList {
+			_ = conn.SetWriteDeadline(time.Now().Add(time.Second * 30))
+			if _, err := conn.WriteTo(buf, remoteAddr); err != nil {
+				return err
+			}
+		}
+		return nil
+	}
+	return errors.Join(do(v4connList, mdnsV4Addr), do(v6connList, mdnsV6Addr))
+}
+
+func multicastInterfaces() ([]net.Interface, error) {
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+	interfaces := make([]net.Interface, 0, len(ifaces))
+	for _, ifi := range ifaces {
+		if (ifi.Flags & net.FlagUp) == 0 {
+			continue
+		}
+		if (ifi.Flags & net.FlagMulticast) > 0 {
+			interfaces = append(interfaces, ifi)
+		}
+	}
+	return interfaces, nil
+}

internal/clientinfo/mdns_services.go

@@ -0,0 +1,70 @@
+package clientinfo
+
+var services = [...]string{
+	// From: https://jonathanmumm.com/tech-it/mdns-bonjour-bible-common-service-strings-for-various-vendors/
+	"_afpovertcp._tcp.local.",
+	"_airdroid._tcp.local.",
+	"_airdrop._tcp.local.",
+	"_airplay._tcp.local.",
+	"_airport._tcp.local.",
+	"_amzn-wplay._tcp.local.",
+	"_sub._apple-mobdev2._tcp.local.",
+	"_apple-mobdev2._tcp.local.",
+	"_apple-sasl._tcp.local.",
+	"_atc._tcp.local.",
+	"_sketchmirror._tcp.local.",
+	"_bp2p._tcp.local.",
+	"_Friendly._sub._bp2p._tcp.local.",
+	"_invoke._sub._bp2p._tcp.local.",
+	"_webdav._sub._bp2p._tcp.local.",
+	"_device-info._tcp.local.",
+	"_distcc._tcp.local.",
+	"_dpap._tcp.local.",
+	"_eppc._tcp.local.",
+	"_esdevice._tcp.local.",
+	"_esfileshare._tcp.local.",
+	"_ftp._tcp.local.",
+	"_googlecast._tcp.local.",
+	"_googlezone._tcp.local.",
+	"_hap._tcp.local.",
+	"_homekit._tcp.local.",
+	"_home-sharing._tcp.local.",
+	"_http._tcp.local.",
+	"_hudson._tcp.local.",
+	"_ica-networking._tcp.local.",
+	"_print._sub._ipp._tcp.local.",
+	"_cups._sub._ipps._tcp.local.",
+	"_print._sub._ipps._tcp.local.",
+	"_jenkins._tcp.local.",
+	"_KeynoteControl._tcp.local.",
+	"_keynotepair._tcp.local.",
+	"_mediaremotetv._tcp.local.",
+	"_nfs._tcp.local.",
+	"_nvstream._tcp.local.",
+	"_androidtvremote._tcp.local.",
+	"_omnistate._tcp.local.",
+	"_photoshopserver._tcp.local.",
+	"_printer._tcp.local.",
+	"_raop._tcp.local.",
+	"_readynas._tcp.local.",
+	"_rfb._tcp.local.",
+	"_physicalweb._tcp.local.",
+	"_rsp._tcp.local.",
+	"_scanner._tcp.local.",
+	"_sftp-ssh._tcp.local.",
+	"_sleep-proxy._udp.local.",
+	"_smb._tcp.local.",
+	"_spotify-connect._tcp.local.",
+	"_ssh._tcp.local.",
+	"_teamviewer._tcp.local.",
+	"_telnet._tcp.local.",
+	"_touch-able._tcp.local.",
+	"_tunnel._tcp.local.",
+	"_webdav._tcp.local.",
+	"_webdav._tcp.local.",
+	"_workstation._tcp.local.",
+	"_xserveraid._tcp.local.",
+
+	// Merlin
+	"_alexa._tcp",
+}

internal/clientinfo/merlin.go

@@ -0,0 +1,67 @@
+package clientinfo
+
+import (
+	"strings"
+	"sync"
+
+	"github.com/Control-D-Inc/ctrld/internal/router"
+	"github.com/Control-D-Inc/ctrld/internal/router/merlin"
+
+	"github.com/Control-D-Inc/ctrld"
+	"github.com/Control-D-Inc/ctrld/internal/router/nvram"
+)
+
+const merlinNvramCustomClientListKey = "custom_clientlist"
+
+type merlinDiscover struct {
+	hostname sync.Map // mac => hostname
+}
+
+func (m *merlinDiscover) refresh() error {
+	if router.Name() != merlin.Name {
+		return nil
+	}
+	out, err := nvram.Run("get", merlinNvramCustomClientListKey)
+	if err != nil {
+		return err
+	}
+	ctrld.ProxyLog.Debug().Msg("reading Merlin custom client list")
+	m.parseMerlinCustomClientList(out)
+	return nil
+}
+
+func (m *merlinDiscover) LookupHostnameByIP(ip string) string {
+	return ""
+}
+
+func (m *merlinDiscover) LookupHostnameByMac(mac string) string {
+	val, ok := m.hostname.Load(mac)
+	if !ok {
+		return ""
+	}
+	return val.(string)
+}
+
+// "nvram get custom_clientlist" output:
+//
+// <client 1>00:00:00:00:00:01>0>4>><client 2>00:00:00:00:00:02>0>24>>...
+//
+// So to parse it, do the following steps:
+//
+//   - Split by "<"                 => entries
+//   - For each entry, split by ">" => parts
+//   - Empty parts                  => skip
+//   - Empty parts[0]               => skip empty hostname
+//   - Empty parts[1]               => skip empty MAC
+func (m *merlinDiscover) parseMerlinCustomClientList(data string) {
+	entries := strings.Split(data, "<")
+	for _, entry := range entries {
+		parts := strings.SplitN(string(entry), ">", 3)
+		if len(parts) < 2 || len(parts[0]) == 0 || len(parts[1]) == 0 {
+			continue
+		}
+		hostname := normalizeHostname(parts[0])
+		mac := strings.ToLower(parts[1])
+		m.hostname.Store(mac, hostname)
+	}
+}

internal/clientinfo/merlin_test.go

@@ -0,0 +1,82 @@
+package clientinfo
+
+import (
+	"testing"
+)
+
+func TestParseMerlinCustomClientList(t *testing.T) {
+	tests := []struct {
+		name              string
+		clientList        string
+		macList           []string
+		hostnameList      []string
+		macNotPresentList []string
+	}{
+		{
+			"normal",
+			"<client1>00:00:00:00:00:01>0>4>>",
+			[]string{"00:00:00:00:00:01"},
+			[]string{"client1"},
+			nil,
+		},
+		{
+			"multiple clients",
+			"<client1>00:00:00:00:00:01>0>4>><client2>00:00:00:00:00:02>0>24>>",
+			[]string{"00:00:00:00:00:01", "00:00:00:00:00:02"},
+			[]string{"client1", "client2"},
+			nil,
+		},
+		{
+			"empty hostname",
+			"<client1>00:00:00:00:00:01>0>4>><>00:00:00:00:00:02>0>24>>",
+			[]string{"00:00:00:00:00:01"},
+			[]string{"client1"},
+			[]string{"00:00:00:00:00:02"},
+		},
+		{
+			"empty dhcp",
+			"<client1>00:00:00:00:00:01>0>4>><client 1>>>",
+			[]string{"00:00:00:00:00:01"},
+			[]string{"client1"},
+			[]string{""},
+		},
+		{
+			"invalid",
+			"qwerty",
+			nil,
+			nil,
+			nil,
+		},
+		{
+			"empty",
+			"",
+
+			nil,
+			nil,
+			nil,
+		},
+	}
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			m := &merlinDiscover{}
+			m.parseMerlinCustomClientList(tc.clientList)
+			for i, mac := range tc.macList {
+				val, ok := m.hostname.Load(mac)
+				if !ok {
+					t.Errorf("missing hostname: %s", mac)
+				}
+				hostname := val.(string)
+				if hostname != tc.hostnameList[i] {
+					t.Errorf("hostname mismatch, want: %q, got: %q", tc.hostnameList[i], hostname)
+				}
+			}
+			for _, mac := range tc.macNotPresentList {
+				if _, ok := m.hostname.Load(mac); ok {
+					t.Errorf("mac2name address %q should not be present", mac)
+				}
+			}
+		})
+	}
+}

internal/clientinfo/ptr_lookup.go

@@ -0,0 +1,62 @@
+package clientinfo
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	"github.com/miekg/dns"
+
+	"github.com/Control-D-Inc/ctrld"
+)
+
+type ptrDiscover struct {
+	hostname sync.Map // ip => hostname
+	resolver ctrld.Resolver
+}
+
+func (p *ptrDiscover) refresh() error {
+	p.hostname.Range(func(key, value any) bool {
+		ip := key.(string)
+		if name := p.lookupHostname(ip); name != "" {
+			p.hostname.Store(ip, name)
+		}
+		return true
+	})
+	return nil
+}
+
+func (p *ptrDiscover) LookupHostnameByIP(ip string) string {
+	if val, ok := p.hostname.Load(ip); ok {
+		return val.(string)
+	}
+	return p.lookupHostname(ip)
+}
+func (p *ptrDiscover) LookupHostnameByMac(mac string) string {
+	return ""
+}
+
+func (p *ptrDiscover) lookupHostname(ip string) string {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	msg := new(dns.Msg)
+	addr, err := dns.ReverseAddr(ip)
+	if err != nil {
+		ctrld.ProxyLog.Error().Err(err).Msg("invalid ip address")
+		return ""
+	}
+	msg.SetQuestion(addr, dns.TypePTR)
+	ans, err := p.resolver.Resolve(ctx, msg)
+	if err != nil {
+		ctrld.ProxyLog.Error().Err(err).Msg("could not lookup IP")
+		return ""
+	}
+	for _, rr := range ans.Answer {
+		if ptr, ok := rr.(*dns.PTR); ok {
+			hostname := normalizeHostname(ptr.Ptr)
+			p.hostname.Store(ip, hostname)
+			return hostname
+		}
+	}
+	return ""
+}

resolver.go

@@ -110,18 +110,6 @@ func (o *osResolver) Resolve(ctx context.Context, msg *dns.Msg) (*dns.Msg, error
 	return nil, errors.Join(errs...)
 }
 
-func newDialer(dnsAddress string) *net.Dialer {
-	return &net.Dialer{
-		Resolver: &net.Resolver{
-			PreferGo: true,
-			Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
-				d := net.Dialer{}
-				return d.DialContext(ctx, network, dnsAddress)
-			},
-		},
-	}
-}
-
 type legacyResolver struct {
 	uc *UpstreamConfig
 }
@@ -149,6 +137,14 @@ func (r *legacyResolver) Resolve(ctx context.Context, msg *dns.Msg) (*dns.Msg, e
 	return answer, err
 }
 
+type dummyResolver struct{}
+
+func (d dummyResolver) Resolve(ctx context.Context, msg *dns.Msg) (*dns.Msg, error) {
+	ans := new(dns.Msg)
+	ans.SetReply(msg)
+	return ans, nil
+}
+
 // LookupIP looks up host using OS resolver.
 // It returns a slice of that host's IPv4 and IPv6 addresses.
 func LookupIP(domain string) []string {
@@ -160,7 +156,7 @@ func lookupIP(domain string, timeout int, withBootstrapDNS bool) (ips []string)
 	if withBootstrapDNS {
 		resolver.nameservers = append([]string{net.JoinHostPort(bootstrapDNS, "53")}, resolver.nameservers...)
 	}
-	ProxyLog.Debug().Msgf("Resolving %q using bootstrap DNS %q", domain, resolver.nameservers)
+	ProxyLog.Debug().Msgf("resolving %q using bootstrap DNS %q", domain, resolver.nameservers)
 	timeoutMs := 2000
 	if timeout > 0 && timeout < timeoutMs {
 		timeoutMs = timeout
@@ -230,7 +226,6 @@ func lookupIP(domain string, timeout int, withBootstrapDNS bool) (ips []string)
 
 // NewBootstrapResolver returns an OS resolver, which use following nameservers:
 //
-//   - ControlD bootstrap DNS server.
 //   - Gateway IP address (depends on OS).
 //   - Input servers.
 func NewBootstrapResolver(servers ...string) Resolver {
@@ -241,3 +236,36 @@ func NewBootstrapResolver(servers ...string) Resolver {
 	}
 	return resolver
 }
+
+// NewPrivateResolver returns an OS resolver, which includes only private DNS servers.
+// This is useful for doing PTR lookup in LAN network.
+func NewPrivateResolver() Resolver {
+	nss := nameservers()
+	n := 0
+	for _, ns := range nss {
+		host, _, _ := net.SplitHostPort(ns)
+		ip := net.ParseIP(host)
+		if ip != nil && ip.IsPrivate() && !ip.IsLoopback() {
+			nss[n] = ns
+			n++
+		}
+	}
+	nss = nss[:n]
+	if len(nss) == 0 {
+		return &dummyResolver{}
+	}
+	resolver := &osResolver{nameservers: nss}
+	return resolver
+}
+
+func newDialer(dnsAddress string) *net.Dialer {
+	return &net.Dialer{
+		Resolver: &net.Resolver{
+			PreferGo: true,
+			Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
+				d := net.Dialer{}
+				return d.DialContext(ctx, network, dnsAddress)
+			},
+		},
+	}
+}