[management] Streamline domain validation (#5211)

client/internal/dns/handler_chain_test.go

@@ -112,6 +112,54 @@ func TestHandlerChain_ServeDNS_DomainMatching(t *testing.T) {
 			matchSubdomains: false,
 			shouldMatch:     false,
 		},
+		{
+			name:            "single letter TLD exact match",
+			handlerDomain:   "example.x.",
+			queryDomain:     "example.x.",
+			isWildcard:      false,
+			matchSubdomains: false,
+			shouldMatch:     true,
+		},
+		{
+			name:            "single letter TLD subdomain match",
+			handlerDomain:   "example.x.",
+			queryDomain:     "sub.example.x.",
+			isWildcard:      false,
+			matchSubdomains: true,
+			shouldMatch:     true,
+		},
+		{
+			name:            "single letter TLD wildcard match",
+			handlerDomain:   "*.example.x.",
+			queryDomain:     "sub.example.x.",
+			isWildcard:      true,
+			matchSubdomains: false,
+			shouldMatch:     true,
+		},
+		{
+			name:            "two letter domain labels",
+			handlerDomain:   "a.b.",
+			queryDomain:     "a.b.",
+			isWildcard:      false,
+			matchSubdomains: false,
+			shouldMatch:     true,
+		},
+		{
+			name:            "single character domain",
+			handlerDomain:   "x.",
+			queryDomain:     "x.",
+			isWildcard:      false,
+			matchSubdomains: false,
+			shouldMatch:     true,
+		},
+		{
+			name:            "single character domain with subdomain match",
+			handlerDomain:   "x.",
+			queryDomain:     "sub.x.",
+			isWildcard:      false,
+			matchSubdomains: true,
+			shouldMatch:     true,
+		},
 	}
 
 	for _, tt := range tests {

management/cmd/management.go

@@ -16,13 +16,13 @@ import (
 	"strings"
 	"syscall"
 
-	"github.com/miekg/dns"
 	log "github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
 
 	"github.com/netbirdio/netbird/formatter/hook"
 	"github.com/netbirdio/netbird/management/internals/server"
 	nbconfig "github.com/netbirdio/netbird/management/internals/server/config"
+	nbdomain "github.com/netbirdio/netbird/shared/management/domain"
 	"github.com/netbirdio/netbird/util"
 	"github.com/netbirdio/netbird/util/crypt"
 )
@@ -78,9 +78,8 @@ var (
 				}
 			}
 
-			_, valid := dns.IsDomainName(dnsDomain)
+			if !nbdomain.IsValidDomainNoWildcard(dnsDomain) {
-			if !valid || len(dnsDomain) > 192 {
+				return fmt.Errorf("invalid dns-domain: %s", dnsDomain)
-				return fmt.Errorf("failed parsing the provided dns-domain. Valid status: %t, Length: %d", valid, len(dnsDomain))
 			}
 
 			return nil

management/internals/modules/zones/records/record.go

@@ -6,7 +6,7 @@ import (
 
 	"github.com/rs/xid"
 
-	"github.com/netbirdio/netbird/management/server/util"
+	"github.com/netbirdio/netbird/shared/management/domain"
 	"github.com/netbirdio/netbird/shared/management/http/api"
 )
 
@@ -63,7 +63,7 @@ func (r *Record) Validate() error {
 		return errors.New("record name is required")
 	}
 
-	if !util.IsValidDomain(r.Name) {
+	if !domain.IsValidDomain(r.Name) {
 		return errors.New("invalid record name format")
 	}
 
@@ -81,8 +81,8 @@ func (r *Record) Validate() error {
 			return err
 		}
 	case RecordTypeCNAME:
-		if !util.IsValidDomain(r.Content) {
+		if !domain.IsValidDomainNoWildcard(r.Content) {
-			return errors.New("invalid CNAME record format")
+			return errors.New("invalid CNAME target format")
 		}
 	default:
 		return errors.New("invalid record type, must be A, AAAA, or CNAME")

management/internals/modules/zones/zone.go

@@ -6,7 +6,7 @@ import (
 	"github.com/rs/xid"
 
 	"github.com/netbirdio/netbird/management/internals/modules/zones/records"
-	"github.com/netbirdio/netbird/management/server/util"
+	"github.com/netbirdio/netbird/shared/management/domain"
 	"github.com/netbirdio/netbird/shared/management/http/api"
 )
 
@@ -73,7 +73,7 @@ func (z *Zone) Validate() error {
 		return errors.New("zone name exceeds maximum length of 255 characters")
 	}
 
-	if !util.IsValidDomain(z.Domain) {
+	if !domain.IsValidDomainNoWildcard(z.Domain) {
 		return errors.New("invalid zone domain format")
 	}
 

management/server/account.go

@@ -26,6 +26,7 @@ import (
 	"golang.org/x/exp/maps"
 
 	nbdns "github.com/netbirdio/netbird/dns"
+	nbdomain "github.com/netbirdio/netbird/shared/management/domain"
 	"github.com/netbirdio/netbird/formatter/hook"
 	"github.com/netbirdio/netbird/management/internals/controllers/network_map"
 	nbconfig "github.com/netbirdio/netbird/management/internals/server/config"
@@ -231,7 +232,7 @@ func BuildManager(
 	// enable single account mode only if configured by user and number of existing accounts is not grater than 1
 	am.singleAccountMode = singleAccountModeDomain != "" && accountsCounter <= 1
 	if am.singleAccountMode {
-		if !isDomainValid(singleAccountModeDomain) {
+		if !nbdomain.IsValidDomainNoWildcard(singleAccountModeDomain) {
 			return nil, status.Errorf(status.InvalidArgument, "invalid domain \"%s\" provided for a single account mode. Please review your input for --single-account-mode-domain", singleAccountModeDomain)
 		}
 		am.singleAccountModeDomain = singleAccountModeDomain
@@ -402,7 +403,7 @@ func (am *DefaultAccountManager) validateSettingsUpdate(ctx context.Context, tra
 		return status.Errorf(status.InvalidArgument, "peer login expiration can't be smaller than one hour")
 	}
 
-	if newSettings.DNSDomain != "" && !isDomainValid(newSettings.DNSDomain) {
+	if newSettings.DNSDomain != "" && !nbdomain.IsValidDomainNoWildcard(newSettings.DNSDomain) {
 		return status.Errorf(status.InvalidArgument, "invalid domain \"%s\" provided for DNS domain", newSettings.DNSDomain)
 	}
 
@@ -1691,10 +1692,12 @@ func (am *DefaultAccountManager) SyncPeerMeta(ctx context.Context, peerPubKey st
 	return nil
 }
 
-var invalidDomainRegexp = regexp.MustCompile(`^([a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,}$`)
+// isDomainValid validates public/IDP domains using stricter rules than internal DNS domains.
+// Requires at least 2-char alphabetic TLD and no single-label domains.
+var publicDomainRegexp = regexp.MustCompile(`^([a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,}$`)
 
 func isDomainValid(domain string) bool {
-	return invalidDomainRegexp.MatchString(domain)
+	return publicDomainRegexp.MatchString(domain)
 }
 
 func (am *DefaultAccountManager) onPeersInvalidated(ctx context.Context, accountID string, peerIDs []string) {

management/server/nameserver.go

@@ -3,10 +3,10 @@ package server
 import (
 	"context"
 	"errors"
-	"regexp"
+	"fmt"
+	"strings"
 	"unicode/utf8"
 
-	"github.com/miekg/dns"
 	"github.com/rs/xid"
 
 	nbdns "github.com/netbirdio/netbird/dns"
@@ -15,11 +15,10 @@ import (
 	"github.com/netbirdio/netbird/management/server/permissions/operations"
 	"github.com/netbirdio/netbird/management/server/store"
 	"github.com/netbirdio/netbird/management/server/types"
+	nbdomain "github.com/netbirdio/netbird/shared/management/domain"
 	"github.com/netbirdio/netbird/shared/management/status"
 )
 
-const domainPattern = `^(?i)[a-z0-9]+([\-\.]{1}[a-z0-9]+)*[*.a-z]{1,}$`
-
 var errInvalidDomainName = errors.New("invalid domain name")
 
 // GetNameServerGroup gets a nameserver group object from account and nameserver group IDs
@@ -305,16 +304,18 @@ func validateGroups(list []string, groups map[string]*types.Group) error {
 	return nil
 }
 
-var domainMatcher = regexp.MustCompile(domainPattern)
+// validateDomain validates a nameserver match domain.
-
+// Converts unicode to punycode. Wildcards are not allowed for nameservers.
-func validateDomain(domain string) error {
+func validateDomain(d string) error {
-	if !domainMatcher.MatchString(domain) {
+	if strings.HasPrefix(d, "*.") {
-		return errors.New("domain should consists of only letters, numbers, and hyphens with no leading, trailing hyphens, or spaces")
+		return errors.New("wildcards not allowed")
 	}
 
-	_, valid := dns.IsDomainName(domain)
+	// Nameservers allow trailing dot (FQDN format)
-	if !valid {
+	toValidate := strings.TrimSuffix(d, ".")
-		return errInvalidDomainName
+
+	if _, err := nbdomain.ValidateDomains([]string{toValidate}); err != nil {
+		return fmt.Errorf("%w: %w", errInvalidDomainName, err)
 	}
 
 	return nil

management/server/nameserver_test.go

@@ -901,82 +901,53 @@ func initTestNSAccount(t *testing.T, am *DefaultAccountManager) (*types.Account,
 	return account, nil
 }
 
+// TestValidateDomain tests nameserver-specific domain validation.
+// Core domain validation is tested in shared/management/domain/validate_test.go.
+// This test only covers nameserver-specific behavior: wildcard rejection and unicode support.
 func TestValidateDomain(t *testing.T) {
 	testCases := []struct {
 		name    string
 		domain  string
 		errFunc require.ErrorAssertionFunc
 	}{
+		// Nameserver-specific: wildcards not allowed
 		{
-			name:    "Valid domain name with multiple labels",
+			name:    "Wildcard prefix rejected",
-			domain:  "123.example.com",
+			domain:  "*.example.com",
+			errFunc: require.Error,
+		},
+		{
+			name:    "Wildcard in middle rejected",
+			domain:  "a.*.example.com",
+			errFunc: require.Error,
+		},
+		// Nameserver-specific: unicode converted to punycode
+		{
+			name:    "Unicode domain converted to punycode",
+			domain:  "münchen.de",
 			errFunc: require.NoError,
 		},
 		{
-			name:    "Valid domain name with hyphen",
+			name:    "Unicode domain all labels",
-			domain:  "test-example.com",
+			domain:  "中国.中国",
+			errFunc: require.NoError,
+		},
+		// Basic validation still works (delegates to shared validation)
+		{
+			name:    "Valid multi-label domain",
+			domain:  "example.com",
 			errFunc: require.NoError,
 		},
 		{
-			name:    "Valid domain name with only one label",
+			name:    "Valid single label",
-			domain:  "example",
+			domain:  "internal",
 			errFunc: require.NoError,
 		},
 		{
-			name:    "Valid domain name with trailing dot",
+			name:    "Invalid leading hyphen",
-			domain:  "example.",
-			errFunc: require.NoError,
-		},
-		{
-			name:    "Invalid wildcard domain name",
-			domain:  "*.example",
-			errFunc: require.Error,
-		},
-		{
-			name:    "Invalid domain name with leading dot",
-			domain:  ".com",
-			errFunc: require.Error,
-		},
-		{
-			name:    "Invalid domain name with dot only",
-			domain:  ".",
-			errFunc: require.Error,
-		},
-		{
-			name:    "Invalid domain name with double hyphen",
-			domain:  "test--example.com",
-			errFunc: require.Error,
-		},
-		{
-			name:    "Invalid domain name with a label exceeding 63 characters",
-			domain:  "dnsdnsdnsdnsdnsdnsdnsdnsdnsdnsdnsdnsdnsdnsdnsdnsdnsdnsdnsdnsdnsdns.com",
-			errFunc: require.Error,
-		},
-		{
-			name:    "Invalid domain name starting with a hyphen",
 			domain:  "-example.com",
 			errFunc: require.Error,
 		},
-		{
-			name:    "Invalid domain name ending with a hyphen",
-			domain:  "example.com-",
-			errFunc: require.Error,
-		},
-		{
-			name:    "Invalid domain with unicode",
-			domain:  "example?,.com",
-			errFunc: require.Error,
-		},
-		{
-			name:    "Invalid domain with space before top-level domain",
-			domain:  "space .example.com",
-			errFunc: require.Error,
-		},
-		{
-			name:    "Invalid domain with trailing space",
-			domain:  "example.com ",
-			errFunc: require.Error,
-		},
 	}
 
 	for _, testCase := range testCases {

management/server/networks/resources/manager_test.go

@@ -203,7 +203,7 @@ func Test_CreateResourceFailsWithInvalidAddress(t *testing.T) {
 		NetworkID:   "testNetworkId",
 		Name:        "testResourceId",
 		Description: "description",
-		Address:     "invalid-address",
+		Address:     "-invalid",
 	}
 
 	store, cleanUp, err := store.NewTestStoreFromSQL(context.Background(), "../../testdata/networks.sql", t.TempDir())
@@ -227,9 +227,9 @@ func Test_CreateResourceFailsWithUsedName(t *testing.T) {
 	resource := &types.NetworkResource{
 		AccountID:   "testAccountId",
 		NetworkID:   "testNetworkId",
-		Name:        "testResourceId",
+		Name:        "used-name",
 		Description: "description",
-		Address:     "invalid-address",
+		Address:     "example.com",
 	}
 
 	store, cleanUp, err := store.NewTestStoreFromSQL(context.Background(), "../../testdata/networks.sql", t.TempDir())

management/server/networks/resources/types/resource.go

@@ -4,7 +4,6 @@ import (
 	"errors"
 	"fmt"
 	"net/netip"
-	"regexp"
 
 	"github.com/rs/xid"
 
@@ -166,8 +165,7 @@ func GetResourceType(address string) (NetworkResourceType, string, netip.Prefix,
 		return Host, "", netip.PrefixFrom(ip, ip.BitLen()), nil
 	}
 
-	domainRegex := regexp.MustCompile(`^(\*\.)?([a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}$`)
+	if _, err := nbDomain.ValidateDomains([]string{address}); err == nil {
-	if domainRegex.MatchString(address) {
 		return Domain, address, netip.Prefix{}, nil
 	}
 

management/server/networks/resources/types/resource_test.go

@@ -23,10 +23,12 @@ func TestGetResourceType(t *testing.T) {
 		{"example.com", Domain, false, "example.com", netip.Prefix{}},
 		{"*.example.com", Domain, false, "*.example.com", netip.Prefix{}},
 		{"sub.example.com", Domain, false, "sub.example.com", netip.Prefix{}},
+		{"example.x", Domain, false, "example.x", netip.Prefix{}},
+		{"internal", Domain, false, "internal", netip.Prefix{}},
 		// Invalid inputs
-		{"invalid", "", true, "", netip.Prefix{}},
 		{"1.1.1.1/abc", "", true, "", netip.Prefix{}},
-		{"1234", "", true, "", netip.Prefix{}},
+		{"-invalid.com", "", true, "", netip.Prefix{}},
+		{"", "", true, "", netip.Prefix{}},
 	}
 
 	for _, tt := range tests {

management/server/util/util.go

@@ -1,9 +1,5 @@
 package util
 
-import "regexp"
-
-var domainRegex = regexp.MustCompile(`^(\*\.)?([a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}$`)
-
 // Difference returns the elements in `a` that aren't in `b`.
 func Difference(a, b []string) []string {
 	mb := make(map[string]struct{}, len(b))
@@ -55,9 +51,3 @@ func contains[T comparableObject[T]](slice []T, element T) bool {
 	return false
 }
 
-func IsValidDomain(domain string) bool {
-	if domain == "" {
-		return false
-	}
-	return domainRegex.MatchString(domain)
-}

shared/management/domain/validate.go

@@ -10,7 +10,30 @@ const maxDomains = 32
 
 var domainRegex = regexp.MustCompile(`^(?:\*\.)?(?:(?:xn--)?[a-zA-Z0-9_](?:[a-zA-Z0-9-_]{0,61}[a-zA-Z0-9])?\.)*(?:xn--)?[a-zA-Z0-9](?:[a-zA-Z0-9-_]{0,61}[a-zA-Z0-9])?$`)
 
-// ValidateDomains checks if each domain in the list is valid and returns a punycode-encoded DomainList.
+// IsValidDomain checks if a single domain string is valid.
+// Does not convert unicode to punycode - domain must already be ASCII/punycode.
+// Allows wildcard prefix (*.example.com).
+func IsValidDomain(domain string) bool {
+	if domain == "" {
+		return false
+	}
+	return domainRegex.MatchString(strings.ToLower(domain))
+}
+
+// IsValidDomainNoWildcard checks if a single domain string is valid without wildcard prefix.
+// Use for zone domains and CNAME targets where wildcards are not allowed.
+func IsValidDomainNoWildcard(domain string) bool {
+	if domain == "" {
+		return false
+	}
+	if strings.HasPrefix(domain, "*.") {
+		return false
+	}
+	return domainRegex.MatchString(strings.ToLower(domain))
+}
+
+// ValidateDomains validates domains and converts unicode to punycode.
+// Allows wildcard prefix (*.example.com). Maximum 32 domains.
 func ValidateDomains(domains []string) (List, error) {
 	if len(domains) == 0 {
 		return nil, fmt.Errorf("domains list is empty")
@@ -37,7 +60,10 @@ func ValidateDomains(domains []string) (List, error) {
 	return domainList, nil
 }
 
-// ValidateDomainsList checks if each domain in the list is valid
+// ValidateDomainsList validates domains without punycode conversion.
+// Use this for domains that must already be in ASCII/punycode format (e.g., extra DNS labels).
+// Unlike ValidateDomains, this does not convert unicode to punycode - unicode domains will fail.
+// Allows wildcard prefix (*.example.com). Maximum 32 domains.
 func ValidateDomainsList(domains []string) error {
 	if len(domains) == 0 {
 		return nil

shared/management/domain/validate_test.go

@@ -2,12 +2,16 @@ package domain
 
 import (
 	"fmt"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 )
 
 func TestValidateDomains(t *testing.T) {
+	label63 := strings.Repeat("a", 63)
+	label64 := strings.Repeat("a", 64)
+
 	tests := []struct {
 		name     string
 		domains  []string
@@ -26,6 +30,48 @@ func TestValidateDomains(t *testing.T) {
 			expected: List{"sub.ex-ample.com"},
 			wantErr:  false,
 		},
+		{
+			name:     "Valid uppercase domain normalized to lowercase",
+			domains:  []string{"EXAMPLE.COM"},
+			expected: List{"example.com"},
+			wantErr:  false,
+		},
+		{
+			name:     "Valid mixed case domain",
+			domains:  []string{"ExAmPlE.CoM"},
+			expected: List{"example.com"},
+			wantErr:  false,
+		},
+		{
+			name:     "Single letter TLD",
+			domains:  []string{"example.x"},
+			expected: List{"example.x"},
+			wantErr:  false,
+		},
+		{
+			name:     "Two letter domain labels",
+			domains:  []string{"a.b"},
+			expected: List{"a.b"},
+			wantErr:  false,
+		},
+		{
+			name:     "Single character domain",
+			domains:  []string{"x"},
+			expected: List{"x"},
+			wantErr:  false,
+		},
+		{
+			name:     "Wildcard with single letter TLD",
+			domains:  []string{"*.x"},
+			expected: List{"*.x"},
+			wantErr:  false,
+		},
+		{
+			name:     "Multi-level with single letter labels",
+			domains:  []string{"a.b.c"},
+			expected: List{"a.b.c"},
+			wantErr:  false,
+		},
 		{
 			name:     "Valid Unicode domain",
 			domains:  []string{"münchen.de"},
@@ -45,17 +91,92 @@ func TestValidateDomains(t *testing.T) {
 			wantErr:  false,
 		},
 		{
-			name:     "Invalid domain format",
+			name:     "Valid domain starting with digit",
+			domains:  []string{"123.example.com"},
+			expected: List{"123.example.com"},
+			wantErr:  false,
+		},
+		// Numeric TLDs are allowed for internal/private DNS use cases.
+		// While ICANN doesn't issue all-numeric gTLDs, the DNS protocol permits them
+		// and resolvers like systemd-resolved handle them correctly.
+		{
+			name:     "Numeric TLD allowed",
+			domains:  []string{"example.123"},
+			expected: List{"example.123"},
+			wantErr:  false,
+		},
+		{
+			name:     "Single digit TLD allowed",
+			domains:  []string{"example.1"},
+			expected: List{"example.1"},
+			wantErr:  false,
+		},
+		{
+			name:     "All numeric labels allowed",
+			domains:  []string{"123.456"},
+			expected: List{"123.456"},
+			wantErr:  false,
+		},
+		{
+			name:     "Single numeric label allowed",
+			domains:  []string{"123"},
+			expected: List{"123"},
+			wantErr:  false,
+		},
+		{
+			name:     "Valid domain with double hyphen",
+			domains:  []string{"test--example.com"},
+			expected: List{"test--example.com"},
+			wantErr:  false,
+		},
+		{
+			name:     "Invalid leading hyphen",
 			domains:  []string{"-example.com"},
 			expected: nil,
 			wantErr:  true,
 		},
 		{
-			name:     "Invalid domain format 2",
+			name:     "Invalid trailing hyphen",
 			domains:  []string{"example.com-"},
 			expected: nil,
 			wantErr:  true,
 		},
+		{
+			name:     "Invalid leading dot",
+			domains:  []string{".com"},
+			expected: nil,
+			wantErr:  true,
+		},
+		{
+			name:     "Invalid dot only",
+			domains:  []string{"."},
+			expected: nil,
+			wantErr:  true,
+		},
+		{
+			name:     "Invalid double dot",
+			domains:  []string{"example..com"},
+			expected: nil,
+			wantErr:  true,
+		},
+		{
+			name:     "Invalid special characters",
+			domains:  []string{"example?,.com"},
+			expected: nil,
+			wantErr:  true,
+		},
+		{
+			name:     "Invalid space in domain",
+			domains:  []string{"space .example.com"},
+			expected: nil,
+			wantErr:  true,
+		},
+		{
+			name:     "Invalid trailing space",
+			domains:  []string{"example.com "},
+			expected: nil,
+			wantErr:  true,
+		},
 		{
 			name:     "Multiple domains valid and invalid",
 			domains:  []string{"google.com", "invalid,nbdomain.com", "münchen.de"},
@@ -86,6 +207,30 @@ func TestValidateDomains(t *testing.T) {
 			expected: nil,
 			wantErr:  true,
 		},
+		{
+			name:     "Valid 63 char label (max)",
+			domains:  []string{label63 + ".com"},
+			expected: List{Domain(label63 + ".com")},
+			wantErr:  false,
+		},
+		{
+			name:     "Invalid 64 char label (exceeds max)",
+			domains:  []string{label64 + ".com"},
+			expected: nil,
+			wantErr:  true,
+		},
+		{
+			name:     "Valid 253 char domain (max)",
+			domains:  []string{strings.Repeat("a.", 126) + "a"},
+			expected: List{Domain(strings.Repeat("a.", 126) + "a")},
+			wantErr:  false,
+		},
+		{
+			name:     "Invalid 254+ char domain (exceeds max)",
+			domains:  []string{strings.Repeat("ab.", 85)},
+			expected: nil,
+			wantErr:  true,
+		},
 	}
 
 	for _, tt := range tests {
@@ -118,6 +263,57 @@ func TestValidateDomainsList(t *testing.T) {
 			domains: []string{"sub.ex-ample.com"},
 			wantErr: false,
 		},
+		{
+			name:    "Uppercase domain accepted",
+			domains: []string{"EXAMPLE.COM"},
+			wantErr: false,
+		},
+		{
+			name:    "Single letter TLD",
+			domains: []string{"example.x"},
+			wantErr: false,
+		},
+		{
+			name:    "Two letter domain labels",
+			domains: []string{"a.b"},
+			wantErr: false,
+		},
+		{
+			name:    "Single character domain",
+			domains: []string{"x"},
+			wantErr: false,
+		},
+		{
+			name:    "Wildcard with single letter TLD",
+			domains: []string{"*.x"},
+			wantErr: false,
+		},
+		{
+			name:    "Multi-level with single letter labels",
+			domains: []string{"a.b.c"},
+			wantErr: false,
+		},
+		// Numeric TLDs are allowed for internal/private DNS use cases.
+		{
+			name:    "Numeric TLD allowed",
+			domains: []string{"example.123"},
+			wantErr: false,
+		},
+		{
+			name:    "Single digit TLD allowed",
+			domains: []string{"example.1"},
+			wantErr: false,
+		},
+		{
+			name:    "All numeric labels allowed",
+			domains: []string{"123.456"},
+			wantErr: false,
+		},
+		{
+			name:    "Single numeric label allowed",
+			domains: []string{"123"},
+			wantErr: false,
+		},
 		{
 			name:    "Underscores in labels",
 			domains: []string{"_jabber._tcp.gmail.com"},