diff --git a/EduNetworkBuilder/NetworkInterface.cs b/EduNetworkBuilder/NetworkInterface.cs
index 39a4c16..2ebacbf 100644
--- a/EduNetworkBuilder/NetworkInterface.cs
+++ b/EduNetworkBuilder/NetworkInterface.cs
@@ -102,9 +102,14 @@ namespace EduNetworkBuilder
                 else
                 {
                     if (Tag == VLANTagType.Untagged)
-                        one.Tag = VLANTagType.Forbidden;
+                        one.Tag = VLANTagType.Forbidden;  //Only one untagged port allowed at a time
                     if (Tag == VLANTagType.Tagged && !isPort) //Ports can have multiple tags on one interface
                         one.Tag = VLANTagType.Forbidden;
+                    if (Tag == VLANTagType.Tagged && isPort)
+                    {
+                        if(one.Tag != VLANTagType.Tagged)
+                            one.Tag = VLANTagType.Forbidden; //We cannot have an untagged port and tagged ports at the same time
+                    }
                 }
             }
             if (!foundit)