diff --git a/generate.py b/generate.py
index eb9a4dd..57d85cc 100755
--- a/generate.py
+++ b/generate.py
@@ -138,6 +138,19 @@ def create_roa_entries(route_objects, filter_rules, mode, f):
            elif mode == 'ipv6':
                f.write('route ' + route_object['route6'] + ' max ' + str(allowed_max_len) + ' as ' + origin + ';' + "\n")
 
+def create_valid_network_function(filter_rules, mode, f):
+    f.write('function dn42_is_valid_' + mode + '_network() {\n')
+    f.write('  return net ~ [\n')
+    first_line_written = False
+    for id, filter_rule in filter_rules.items():
+        if filter_rule['route_allowed']:
+            if first_line_written:
+                f.write(',\n')
+            f.write('    ' + filter_rule['network'] + '{' + str(filter_rule['min_length']) + ',' + str(filter_rule['max_length']) + '}')
+            if not first_line_written:
+                first_line_written = True
+    f.write('\n  ];\n')
+    f.write('}\n')
 
 if __name__ == '__main__':
     # Get registry path over commandline argument
@@ -154,8 +167,14 @@ if __name__ == '__main__':
     ipv4_route_objects = parse_route_objects(registry_path + '/data/route/')
     ipv6_route_objects = parse_route_objects(registry_path + '/data/route6/')
     # Create routes out of ipv4 route objects
-    with open('./roa_ipv4.conf', 'w') as target_file:
+    with open('./dn42_roa_ipv4.conf', 'w') as target_file:
         create_roa_entries(ipv4_route_objects, ipv4_filter_rules, 'ipv4', target_file)
     # Create routes out of ipv6 route objects
-    with open('./roa_ipv6.conf', 'w') as target_file:
+    with open('./dn42_roa_ipv6.conf', 'w') as target_file:
         create_roa_entries(ipv6_route_objects, ipv6_filter_rules, 'ipv6', target_file)
+    # Create ipv4 network validation function
+    with open('./dn42_valid_ipv4.conf', 'w') as target_file:
+        create_valid_network_function(ipv4_filter_rules, 'ipv4', target_file)
+    # Create ipv6 network validation function
+    with open('./dn42_valid_ipv6.conf', 'w') as target_file:
+        create_valid_network_function(ipv6_filter_rules, 'ipv6', target_file)