diff --git a/src/topupopt/problems/esipp/network.py b/src/topupopt/problems/esipp/network.py
index 5e12053e74d96231b39831107d71a0f2dcfb43ea..0b257e6b22df89ff3bc35c07e69d469399e8c388 100644
--- a/src/topupopt/problems/esipp/network.py
+++ b/src/topupopt/problems/esipp/network.py
@@ -633,11 +633,19 @@ class Network(nx.MultiDiGraph):
         self.identify_node_types()
 
         # declare variables for the nodes without directed arc limitations
+        if network_type not in self.NET_TYPES:
+            raise ValueError('Unknown network type.')
         self.network_type = network_type
 
         self.nodes_w_in_dir_arc_limitations = dict()
     
         self.nodes_w_out_dir_arc_limitations = dict()
+        
+        # set up initial nodes if the network is not hybrid
+        if self.network_type != self.NET_TYPE_HYBRID:
+            for node_key in self.nodes():
+                self._set_up_node(node_key)
+                
 
     # *************************************************************************
     # *************************************************************************