diff --git a/sets/sets.go b/sets/sets.go
index 0343052..6e6bdbc 100644
--- a/sets/sets.go
+++ b/sets/sets.go
@@ -7,6 +7,7 @@ import (
 	"sync"
 
 	"inet.af/netaddr"
+	v1 "k8s.io/api/core/v1"
 	discoveryv1 "k8s.io/api/discovery/v1"
 	"k8s.io/client-go/informers"
 	"k8s.io/client-go/tools/cache"
@@ -138,8 +139,6 @@ func NewKubernetesSet(ctx context.Context, f informers.SharedInformerFactory, se
 		port = "5060"
 	}
 
-	informer := f.Discovery().V1().EndpointSlices()
-
 	s := &kubernetesSet{
 		id:        setID,
 		namespace: namespace,
@@ -147,6 +146,8 @@ func NewKubernetesSet(ctx context.Context, f informers.SharedInformerFactory, se
 		port:      port,
 	}
 
+	informer := f.Discovery().V1().EndpointSlices()
+
 	informer.Informer().AddEventHandler(cache.ResourceEventHandlerFuncs{
 		AddFunc:    s.addFunc,
 		UpdateFunc: s.updateFunc,
@@ -217,7 +218,7 @@ func (s *kubernetesSet) Close() {}
 
 func (s *kubernetesSet) State() *State {
 	return &State{
-		ID: s.id,
+		ID:        s.id,
 		Endpoints: s.endpoints,
 	}
 }
@@ -245,6 +246,187 @@ func (s *kubernetesSet) IsMember(addr string, port uint32) bool {
 	return false
 }
 
+// legacyKubernetesSet represents a dispatcher set whose
+// data should be derived from Kubernetes.
+type legacyKubernetesSet struct {
+	// id is the dispatch set index for this set
+	id int
+
+	endpoints []*Endpoint
+
+	// callbacks is the set of functions which should be called when the endpoint membership changes.
+	callbacks []func(*State)
+
+	// name is the name of the Kubernetes Endpoint List
+	// from which the dispatcher endpoints should be derived.
+	name string
+
+	// namespace is the namespace in which the Endpoint
+	// should be found.
+	namespace string
+
+	port string
+
+	mu sync.Mutex
+}
+
+// NewLegacyKunbernetesSet returns a new Kubernetes-based dispatcher set using the older Endpoints method.
+// If the server is running an older version of Kubernetes which does not support v1.EndpointSlices (<v1.21), use this Kubernetes set.
+//
+//  * `setID` is the dispatcher set's id
+//
+//  * `namespace` is the namespace of the Service whose endpoints will describe this dispatcher set.
+//
+//  * `name` is the name of the Service whose endpoints will describe this dispatcher set.
+//
+//  * `port` is the port reference of the SIP endpoints this set describes.  This is optional, and if not specified, will default to "5060".
+//
+func NewLegacyKubernetesSet(ctx context.Context, f informers.SharedInformerFactory, setID int, namespace, name, port string) (DispatcherSet, error) {
+	if port == "" {
+		port = "5060"
+	}
+
+	s := &legacyKubernetesSet{
+		id:        setID,
+		namespace: namespace,
+		name:      name,
+		port:      port,
+	}
+
+	informer := f.Core().V1().Endpoints()
+
+	informer.Informer().AddEventHandler(cache.ResourceEventHandlerFuncs{
+		AddFunc:    s.addFunc,
+		UpdateFunc: s.updateFunc,
+		DeleteFunc: s.deleteFunc,
+	})
+
+	go informer.Informer().Run(ctx.Done())
+
+	return s, nil
+}
+
+func (s *legacyKubernetesSet) updateSet(obj interface{}) {
+	epList, ok := obj.(*v1.Endpoints)
+	if !ok {
+		return
+	}
+
+	if epList.Namespace != s.namespace {
+		return
+	}
+
+	if epList.Name != s.name {
+		return
+	}
+
+	list, err := flattenEndpoints(s.port, epList)
+	if err != nil {
+		return
+	}
+
+	s.mu.Lock()
+	if !isChanged(s.endpoints, list) {
+		s.mu.Unlock()
+		return
+	}
+
+	s.endpoints = list
+	s.mu.Unlock()
+
+	state := &State{
+		ID:        s.id,
+		Endpoints: list,
+	}
+
+	for _, f := range s.callbacks {
+		f(state)
+	}
+}
+
+func (s *legacyKubernetesSet) addFunc(obj interface{}) {
+	s.updateSet(obj)
+}
+
+func (s *legacyKubernetesSet) updateFunc(old interface{}, obj interface{}) {
+	s.updateSet(obj)
+}
+
+func (s *legacyKubernetesSet) deleteFunc(obj interface{}) {
+	s.updateSet(obj)
+}
+
+func (s *legacyKubernetesSet) Close() {}
+
+func (s *legacyKubernetesSet) State() *State {
+	return &State{
+		ID:        s.id,
+		Endpoints: s.endpoints,
+	}
+}
+
+func (s *legacyKubernetesSet) RegisterChangeFunc(f func(*State)) {
+	s.mu.Lock()
+
+	s.callbacks = append(s.callbacks, f)
+
+	defer s.mu.Unlock()
+}
+
+func (s *legacyKubernetesSet) IsMember(addr string, port uint32) bool {
+	for _, ep := range s.endpoints {
+		if ep.Address == addr {
+
+			if port > 0 {
+				if ep.Port != port {
+					return false
+				}
+			}
+			return true
+		}
+	}
+	return false
+}
+
+func flattenEndpoints(refPort string, epList *v1.Endpoints) (out []*Endpoint, err error) {
+	parsedPortNumber, err := strconv.Atoi(refPort)
+	if err != nil {
+		parsedPortNumber = 0
+	}
+
+	portNumber := uint32(parsedPortNumber)
+
+	for _, ss := range epList.Subsets {
+
+		if portNumber == 0 {
+			for _, p := range ss.Ports {
+				if p.Name == "" {
+					continue
+				}
+
+				if p.Name == refPort {
+					if p.Port > 0 {
+						portNumber = uint32(p.Port)
+					}
+				}
+			}
+
+			if portNumber == 0 {
+				return nil, fmt.Errorf("failed to find port %s in Endpoints %q", refPort, epList.Name)
+			}
+		}
+
+		for _, addr := range ss.Addresses {
+			out = append(out, &Endpoint{
+				Address: addr.IP,
+				Port:    portNumber,
+			})
+		}
+	}
+
+	return out, nil
+}
+
 func flattenEndpointSlice(refPort string, epSlice *discoveryv1.EndpointSlice) (out []*Endpoint, err error) {
 	portNumber, err := strconv.Atoi(refPort)
 	if err != nil {