diff --git a/pkg/apis/config/defaults.go b/pkg/apis/config/defaults.go
index 368f1be7e6c..f12b83ab534 100644
--- a/pkg/apis/config/defaults.go
+++ b/pkg/apis/config/defaults.go
@@ -85,6 +85,8 @@ type Defaults struct {
 type ClassAndBrokerConfig struct {
 	BrokerClass   string `json:"brokerClass,omitempty"`
 	*BrokerConfig `json:",inline"`
+
+	DisallowDifferentNamespaceConfig *bool `json:"disallowDifferentNamespaceConfig,omitempty"`
 }
 
 // BrokerConfig contains configuration for a given namespace for broker. Allows
diff --git a/pkg/apis/config/zz_generated.deepcopy.go b/pkg/apis/config/zz_generated.deepcopy.go
index a57b366a93b..e02665cc874 100644
--- a/pkg/apis/config/zz_generated.deepcopy.go
+++ b/pkg/apis/config/zz_generated.deepcopy.go
@@ -60,6 +60,11 @@ func (in *ClassAndBrokerConfig) DeepCopyInto(out *ClassAndBrokerConfig) {
 		*out = new(BrokerConfig)
 		(*in).DeepCopyInto(*out)
 	}
+	if in.DisallowDifferentNamespaceConfig != nil {
+		in, out := &in.DisallowDifferentNamespaceConfig, &out.DisallowDifferentNamespaceConfig
+		*out = new(bool)
+		**out = **in
+	}
 	return
 }
 
diff --git a/pkg/apis/eventing/v1/broker_validation.go b/pkg/apis/eventing/v1/broker_validation.go
index d6c4180c689..1829872f9ee 100644
--- a/pkg/apis/eventing/v1/broker_validation.go
+++ b/pkg/apis/eventing/v1/broker_validation.go
@@ -23,6 +23,8 @@ import (
 
 	"knative.dev/pkg/apis"
 	"knative.dev/pkg/kmp"
+
+	"knative.dev/eventing/pkg/apis/config"
 )
 
 const (
@@ -30,7 +32,22 @@ const (
 )
 
 func (b *Broker) Validate(ctx context.Context) *apis.FieldError {
-	withNS := apis.AllowDifferentNamespace(apis.WithinParent(ctx, b.ObjectMeta))
+	ctx = apis.WithinParent(ctx, b.ObjectMeta)
+
+	cfg := config.FromContextOrDefaults(ctx)
+	var brConfig *config.ClassAndBrokerConfig
+	if cfg.Defaults != nil {
+		if c, ok := cfg.Defaults.NamespaceDefaultsConfig[b.GetNamespace()]; ok {
+			brConfig = c
+		} else {
+			brConfig = cfg.Defaults.ClusterDefault
+		}
+	}
+
+	withNS := ctx
+	if brConfig == nil || brConfig.DisallowDifferentNamespaceConfig == nil || !*brConfig.DisallowDifferentNamespaceConfig {
+		withNS = apis.AllowDifferentNamespace(ctx)
+	}
 
 	// Make sure a BrokerClassAnnotation exists
 	var errs *apis.FieldError
diff --git a/pkg/apis/eventing/v1/broker_validation_test.go b/pkg/apis/eventing/v1/broker_validation_test.go
index 2b33739b7ea..ae4dd7e25f9 100644
--- a/pkg/apis/eventing/v1/broker_validation_test.go
+++ b/pkg/apis/eventing/v1/broker_validation_test.go
@@ -18,13 +18,17 @@ package v1
 
 import (
 	"context"
+	"fmt"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
-	eventingduckv1 "knative.dev/eventing/pkg/apis/duck/v1"
+	"k8s.io/utils/pointer"
 	"knative.dev/pkg/apis"
 	duckv1 "knative.dev/pkg/apis/duck/v1"
+
+	"knative.dev/eventing/pkg/apis/config"
+	eventingduckv1 "knative.dev/eventing/pkg/apis/duck/v1"
 )
 
 func TestBrokerImmutableFields(t *testing.T) {
@@ -80,6 +84,7 @@ func TestValidate(t *testing.T) {
 	tests := []struct {
 		name string
 		b    Broker
+		cfg  *config.Config
 		want *apis.FieldError
 	}{{
 		name: "missing annotation",
@@ -187,10 +192,92 @@ func TestValidate(t *testing.T) {
 			},
 		},
 		want: apis.ErrInvalidValue(invalidString, "spec.delivery.backoffDelay"),
+	}, {
+		name: "invalid config, cross namespace disallowed, cluster wide",
+		cfg: &config.Config{
+			Defaults: &config.Defaults{
+				NamespaceDefaultsConfig: nil,
+				ClusterDefault: &config.ClassAndBrokerConfig{
+					DisallowDifferentNamespaceConfig: pointer.Bool(true),
+				},
+			},
+		},
+		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+				Namespace:   "ns1",
+			},
+			Spec: BrokerSpec{
+				Config: &duckv1.KReference{
+					Kind:       "ConfigMap",
+					Namespace:  "ns2",
+					Name:       "cm",
+					APIVersion: "v1",
+				},
+			},
+		},
+		want: &apis.FieldError{
+			Message: "mismatched namespaces",
+			Paths:   []string{"spec.config.namespace"},
+			Details: fmt.Sprintf("parent namespace: %q does not match ref: %q", "ns1", "ns2"),
+		},
+	}, {
+		name: "invalid config, cross namespace disallowed, namespace wide",
+		cfg: &config.Config{
+			Defaults: &config.Defaults{
+				NamespaceDefaultsConfig: map[string]*config.ClassAndBrokerConfig{
+					"ns1": {DisallowDifferentNamespaceConfig: pointer.Bool(true)},
+				},
+			},
+		},
+		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+				Namespace:   "ns1",
+			},
+			Spec: BrokerSpec{
+				Config: &duckv1.KReference{
+					Kind:       "ConfigMap",
+					Namespace:  "ns2",
+					Name:       "cm",
+					APIVersion: "v1",
+				},
+			},
+		},
+		want: &apis.FieldError{
+			Message: "mismatched namespaces",
+			Paths:   []string{"spec.config.namespace"},
+			Details: fmt.Sprintf("parent namespace: %q does not match ref: %q", "ns1", "ns2"),
+		},
+	}, {
+		name: "valid config, cross namespace allowed, namespace wide",
+		cfg: &config.Config{
+			Defaults: &config.Defaults{
+				NamespaceDefaultsConfig: map[string]*config.ClassAndBrokerConfig{
+					"ns1": {DisallowDifferentNamespaceConfig: pointer.Bool(true)},
+				},
+			},
+		},
+		b: Broker{
+			ObjectMeta: metav1.ObjectMeta{
+				Annotations: map[string]string{"eventing.knative.dev/broker.class": "MTChannelBasedBroker"},
+				Namespace:   "ns2",
+			},
+			Spec: BrokerSpec{
+				Config: &duckv1.KReference{
+					Kind:       "ConfigMap",
+					Namespace:  "ns3",
+					Name:       "cm",
+					APIVersion: "v1",
+				},
+			},
+		},
+		want: nil,
 	}}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			got := test.b.Validate(context.Background())
+			ctx := config.ToContext(context.Background(), test.cfg)
+			got := test.b.Validate(ctx)
 			if diff := cmp.Diff(test.want.Error(), got.Error()); diff != "" {
 				t.Error("Broker.Validate (-want, +got) =", diff)
 			}