Add --dry-with-dhcp option

README.md

@@ -83,7 +83,8 @@ For more information, run `pretender --help`.
 - If you are not sure which interface to choose (especially on Windows), list
   all interfaces with names and addresses using `--interfaces`
 - If you want to exclude hosts from local name resolution spoofing, make sure to
-  also exclude their IPv6 addresses or use `--no-ipv6-lnr`/`main.vendorNoIPv6LNR`
+  also exclude their IPv6 addresses or use
+  `--no-ipv6-lnr`/`main.vendorNoIPv6LNR`
 - DHCPv6 messages usually contain a FQDN option (which can also sometimes
   contain a hostname which is not a FQDN). This option is used to filter out
   messages by hostname (`--spoof-for`/`--dont-spoof-for`). You can decide what
@@ -109,7 +110,8 @@ For more information, run `pretender --help`.
 - By default, in order to limit disruption during a DHCPv6 DNS Takeover, the
   option `--delegate-ignored-to <DNS server>` can be used to delegate ignored
   queries to a legitimate DNS server.
-
+- The option `--dry-with-dhcp` can be combined with `--delegate-ignored-to` to
+  monitor the name resolution queries in the network without disruption.
 ---
 
 ## Building and Vendoring
@@ -160,6 +162,7 @@ vendorIgnoreDHCPv6NoFQDN
 vendorDelegateIgnoredTo
 vendorDontSendEmptyReplies
 vendorDryMode
+vendorDryWithDHCPMode
 vendorTTL
 vendorLeaseLifetime
 vendorRARouterLifetime

cli.go

@@ -47,7 +47,7 @@ type Config struct {
 	DelegateIgnoredTo    string
 	DontSendEmptyReplies bool
 	DryMode              bool
-	DryWithDHCPv6        bool
+	DryWithDHCPv6Mode    bool
 
 	StopAfter      time.Duration
 	Verbose        bool
@@ -88,13 +88,17 @@ func (c Config) PrintSummary() { //nolint:cyclop
 
 	switch {
 	case c.DryMode:
-		var raNotice string
-
+		raNotice := ""
 		if !c.NoRA && !c.NoDHCPv6DNSTakeover && !c.NoDHCPv6 {
 			raNotice = " (RA is still enabled)"
 		}
 
-		fmt.Println("Dry Mode: DHCPv6 and name resolution queries will not be answered" + raNotice)
+		drySubject := "DHCPv6 and name resolution queries"
+		if c.DryWithDHCPv6Mode {
+			drySubject = "Name resolution queries"
+		}
+
+		fmt.Printf("Dry Mode: %s will not be answered%s\n", drySubject, raNotice)
 	default:
 		if len(c.Spoof) != 0 {
 			fmt.Println("Answering queries for: " + joinDomains(c.Spoof))
@@ -128,7 +132,27 @@ func (c Config) PrintSummary() { //nolint:cyclop
 	fmt.Println()
 }
 
-//nolint:forbidigo,cyclop,maintidx
+func (c *Config) setRedundantOptions() {
+	if c.DryWithDHCPv6Mode {
+		c.DryMode = true
+	}
+
+	if c.NoDNS && c.NoDHCPv6 {
+		c.NoDHCPv6DNSTakeover = true
+	}
+
+	if c.NoMDNS && c.NoLLMNR && c.NoNetBIOS {
+		c.NoLocalNameResolution = true
+	}
+
+	if c.NoLocalNameResolution {
+		c.NoNetBIOS = true
+		c.NoLLMNR = true
+		c.NoMDNS = true
+	}
+}
+
+//nolint:forbidigo,cyclop
 func configFromCLI() (config Config, logger *Logger, err error) {
 	var (
 		interfaceName string
@@ -178,8 +202,11 @@ func configFromCLI() (config Config, logger *Logger, err error) {
 	pflag.BoolVar(&config.DontSendEmptyReplies, "dont-send-empty-replies", defaultDontSendEmptyReplies,
 		"Don't reply at all to ignored DNS queries or failed delegated\nqueries instead of sending an empty reply")
 	pflag.BoolVar(&config.DryMode, "dry", defaultDryMode,
-		"Do not spoof name resolution at all, only log queries (does not disable\nRA but it"+
-			" can be combined with --no-ra)")
+		"Do not answer DHCPv6 or any name resolution queries, only log them\n(does not disable RA but it "+
+			"can be combined with --no-ra)")
+	pflag.BoolVar(&config.DryWithDHCPv6Mode, "dry-with-dhcp", defaultDryWithDHCPMode,
+		"Send RA and answer DHCPv6 queries but only log name resolution\nqueries (can be"+
+			" combined with --delegate-ignored-to, takes\nprecedence over --dry)")
 
 	pflag.DurationVarP(&config.TTL, "ttl", "t", defaultTTL, "Time to live for name resolution responses")
 	pflag.DurationVar(&config.LeaseLifetime, "lease-lifetime", defaultLeaseLifetime, "DHCPv6 IP lease lifetime")
@@ -216,19 +243,7 @@ func configFromCLI() (config Config, logger *Logger, err error) {
 		stdErr = os.Stdout
 	}
 
-	if config.NoDNS && config.NoDHCPv6 {
-		config.NoDHCPv6DNSTakeover = true
-	}
-
-	if config.NoMDNS && config.NoLLMNR && config.NoNetBIOS {
-		config.NoLocalNameResolution = true
-	}
-
-	if config.NoLocalNameResolution {
-		config.NoNetBIOS = true
-		config.NoLLMNR = true
-		config.NoMDNS = true
-	}
+	config.setRedundantOptions()
 
 	if printVersion {
 		fmt.Println(longVersion())

defaults.go

@@ -38,6 +38,7 @@ var (
 	vendorDelegateIgnoredTo    = ""
 	vendorDontSendEmptyReplies = ""
 	vendorDryMode              = ""
+	vendorDryWithDHCPMode      = ""
 
 	vendorTTL              = ""
 	vendorLeaseLifetime    = ""
@@ -81,6 +82,7 @@ var (
 	defaultDelegateIgnoredTo    = vendorDelegateIgnoredTo
 	defaultDontSendEmptyReplies = forceBool(vendorDontSendEmptyReplies, false)
 	defaultDryMode              = forceBool(vendorDryMode, false)
+	defaultDryWithDHCPMode      = forceBool(vendorDryWithDHCPMode, false)
 
 	defaultTTL              = forceDuration(vendorTTL, dnsDefaultTTL)
 	defaultLeaseLifetime    = forceDuration(vendorLeaseLifetime, dhcpv6DefaultValidLifetime)

filter.go

@@ -94,7 +94,7 @@ func shouldRespondToNameResolutionQuery(config Config, host string, queryType ui
 }
 
 func shouldRespondToDHCP(config Config, from peerInfo) (bool, string) {
-	if config.DryMode {
+	if config.DryMode && !config.DryWithDHCPv6Mode {
 		return false, "dry mode"
 	}
 

filter_test.go

@@ -22,6 +22,7 @@ func TestFilterNameResolutionQuery(t *testing.T) { //nolint:maintidx,cyclop
 		DontSpoof             []string
 		SpoofTypes            []string
 		DryMode               bool
+		DryWithDHCPv6Mode     bool
 		NoRelayIPv4Configured bool
 		NoRelayIPv6Configured bool
 
@@ -53,6 +54,13 @@ func TestFilterNameResolutionQuery(t *testing.T) { //nolint:maintidx,cyclop
 			From:          someIP,
 			ShouldRespond: false,
 		},
+		{
+			TestName:          "dry with dhcp",
+			Host:              "foo",
+			DryWithDHCPv6Mode: true,
+			From:              someIP,
+			ShouldRespond:     false,
+		},
 		{
 			Host:          "foo",
 			Spoof:         []string{"foo"},
@@ -332,15 +340,18 @@ func TestFilterNameResolutionQuery(t *testing.T) { //nolint:maintidx,cyclop
 			}
 
 			cfg := Config{
-				SpoofFor:     asHostMatchers(testCase.SpoofFor, defaultLookupTimeout),
-				DontSpoofFor: asHostMatchers(testCase.DontSpoofFor, defaultLookupTimeout),
-				Spoof:        testCase.Spoof,
-				DontSpoof:    testCase.DontSpoof,
-				DryMode:      testCase.DryMode,
-				SpoofTypes:   types,
-				SOAHostname:  "test",
+				SpoofFor:          asHostMatchers(testCase.SpoofFor, defaultLookupTimeout),
+				DontSpoofFor:      asHostMatchers(testCase.DontSpoofFor, defaultLookupTimeout),
+				Spoof:             testCase.Spoof,
+				DontSpoof:         testCase.DontSpoof,
+				DryMode:           testCase.DryMode,
+				DryWithDHCPv6Mode: testCase.DryWithDHCPv6Mode,
+				SpoofTypes:        types,
+				SOAHostname:       "test",
 			}
 
+			cfg.setRedundantOptions()
+
 			switch {
 			case !testCase.NoRelayIPv4Configured:
 				cfg.RelayIPv4 = relayIPv4
@@ -376,6 +387,7 @@ func TestFilterDHCP(t *testing.T) {
 		DontSpoofFor       []string
 		IgnoreDHCPv6NoFQDN bool
 		DryMode            bool
+		DryWithDHCPv6Mode  bool
 
 		PeerIP        net.IP
 		PeerHostnames []string
@@ -395,6 +407,21 @@ func TestFilterDHCP(t *testing.T) {
 			PeerHostnames: []string{"foo"},
 			ShouldRespond: false,
 		},
+		{
+			TestName:          "dry with dhcp",
+			DryWithDHCPv6Mode: true,
+			PeerIP:            someIP,
+			PeerHostnames:     []string{"foo"},
+			ShouldRespond:     true,
+		},
+		{
+			TestName:          "dry and drywith dhcp",
+			DryMode:           true,
+			DryWithDHCPv6Mode: true,
+			PeerIP:            someIP,
+			PeerHostnames:     []string{"foo"},
+			ShouldRespond:     true,
+		},
 		{
 			TestName:      "dry+spooffor",
 			SpoofFor:      []string{someIP.String(), "foo"},
@@ -469,9 +496,12 @@ func TestFilterDHCP(t *testing.T) {
 				SpoofFor:           asHostMatchers(testCase.SpoofFor, defaultLookupTimeout),
 				DontSpoofFor:       asHostMatchers(testCase.DontSpoofFor, defaultLookupTimeout),
 				DryMode:            testCase.DryMode,
+				DryWithDHCPv6Mode:  testCase.DryWithDHCPv6Mode,
 				IgnoreDHCPv6NoFQDN: testCase.IgnoreDHCPv6NoFQDN,
 			}
 
+			cfg.setRedundantOptions()
+
 			shouldRespond, _ := shouldRespondToDHCP(cfg,
 				peerInfo{IP: testCase.PeerIP, Hostnames: testCase.PeerHostnames})
 			if shouldRespond != testCase.ShouldRespond {