diff --git a/libnetwork/endpoint.go b/libnetwork/endpoint.go
index 55b3a8e1ab..7608dd7457 100644
--- a/libnetwork/endpoint.go
+++ b/libnetwork/endpoint.go
@@ -477,6 +477,10 @@ func (ep *endpoint) sbJoin(sb *sandbox, options ...EndpointOption) error {
 					ep.Name(), ep.ID(), err)
 			}
 		}
+
+		if sb.resolver != nil {
+			sb.resolver.FlushExtServers()
+		}
 	}
 
 	if !sb.needDefaultGW() {
diff --git a/libnetwork/resolver.go b/libnetwork/resolver.go
index a54a967770..cff692fd1f 100644
--- a/libnetwork/resolver.go
+++ b/libnetwork/resolver.go
@@ -158,6 +158,10 @@ func (r *resolver) Start() error {
 
 func (r *resolver) FlushExtServers() {
 	for i := 0; i < maxExtDNS; i++ {
+		if r.extDNSList[i].extConn != nil {
+			r.extDNSList[i].extConn.Close()
+		}
+
 		r.extDNSList[i].extConn = nil
 		r.extDNSList[i].extOnce = sync.Once{}
 	}