diff --git a/cmd/default-domain/domain_test.go b/cmd/default-domain/domain_test.go
new file mode 100644
index 000000000000..8663e3edd73e
--- /dev/null
+++ b/cmd/default-domain/domain_test.go
@@ -0,0 +1,47 @@
+/*
+Copyright 2024 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+import "testing"
+
+func TestBuildMagicDNSName(t *testing.T) {
+	for _, tt := range []struct {
+		name     string
+		magicDNS string
+		ip       string
+		want     string
+	}{
+		{
+			name:     "ipv4",
+			magicDNS: "sslip.io",
+			ip:       "1.1.1.1",
+			want:     "1.1.1.1.sslip.io",
+		},
+		{
+			name:     "ipv6",
+			magicDNS: "sslip.io",
+			ip:       "2a01:4f8:c17:b8f::2",
+			want:     "2a01-4f8-c17-b8f--2.sslip.io",
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := buildMagicDNSName(tt.ip, tt.magicDNS); got != tt.want {
+				t.Errorf("buildMagicDNSName() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
diff --git a/cmd/default-domain/main.go b/cmd/default-domain/main.go
index 00f6a86f7971..ec2f6f6cdd15 100644
--- a/cmd/default-domain/main.go
+++ b/cmd/default-domain/main.go
@@ -164,6 +164,13 @@ func findGatewayAddress(ctx context.Context, kubeclient kubernetes.Interface, cl
 	return &svc.Status.LoadBalancer.Ingress[0], nil
 }
 
+func buildMagicDNSName(ip, magicDNS string) string {
+	if magicDNS == "sslip.io" {
+		ip = strings.ReplaceAll(ip, ":", "-")
+	}
+	return fmt.Sprintf("%s.%s", ip, magicDNS)
+}
+
 func main() {
 	flag.Parse()
 	ctx := signals.NewContext()
@@ -209,19 +216,21 @@ func main() {
 			logger.Info("Gateway has neither IP nor hostname -- leaving default domain config intact")
 			return
 		}
-		ipAddr, err := net.ResolveIPAddr("ip4", address.Hostname)
+		ipAddr, err := net.ResolveIPAddr("ip", address.Hostname)
 		if err != nil {
 			logger.Fatalw("Error resolving the IP address of %q", address.Hostname, zap.Error(err))
 		}
 		ip = ipAddr.String()
 	}
 
-	// Use the IP (assumes IPv4) to set up a magic DNS name under a top-level Magic
+	// Use the IP to set up a magic DNS name under a top-level Magic
 	// DNS service like sslip.io or nip.io, where:
 	//     1.2.3.4.sslip.io  ===(magically resolves to)===> 1.2.3.4
+	//     2a01-4f8-c17-b8f--2.sslip.io ===(magically resolves to)===> 2a01:4f8:c17:b8f::2
+	//
 	// Add this magic DNS name without a label selector to the ConfigMap,
 	// and send it back to the API server.
-	domain := fmt.Sprintf("%s.%s", ip, *magicDNS)
+	domain := buildMagicDNSName(ip, *magicDNS)
 	domainCM.Data[domain] = ""
 	if _, err = kubeClient.CoreV1().ConfigMaps(system.Namespace()).Update(ctx, domainCM, metav1.UpdateOptions{}); err != nil {
 		logger.Fatalw("Error updating ConfigMap", zap.Error(err))