Se agrega next-server en config kea

src/KeaBundle/Services/BaseKea.php

@@ -83,6 +83,12 @@ class BaseKea implements KeaConfigInterface
                 'subnet' => $subnet->getAddress(),
                 'pools' => $pools,
             ];
+            
+            $nextServer = $subnet->getNextServer();
+            if ($nextServer != '') {
+                $subnetConf['next-server'] = $nextServer;
+            }
+            
             if ($client_class != '') {
                 $subnetConf['client-class'] = $client_class;
             }