ntegrity. A solution could look like this: The communication system is built in three layers. A transport IP part, a secure data communication network and an application layer with management support applica- tions. Access is possible only by means of specific logon servers. A public key server is used to generate certificates. The CORBA traffic is secured by means of security modules at application level in the nodes, verifying authority and authenticity. Telnet and FTP traffic are protected by means of SSH/TLS. Security information is stored in a LDAP server. Security for Network Resources Network resources are normally controlled by the management system. As long as the management system is run by authorized staff there is only the human factor that could cause harm to the network through the management system. Making sure that only autho- rized staff can access the management system can be achieved by means of digital certificate based on secure encryption. Then there are threats from physical damage. A third threat comes from the service network, which could control network resources via the API interfaces. Therefore an authorization/authentication procedure protecting the network is provided in the service network (application)-control interface. A similar protection is required in the user-service network (application) interface. As mentioned in the introduction, integrity targets are supported by the separation and protection of resources. In order to control the security, network security partitioning into zones should be used for large networks. The borders might be points where protection method changes, for example from L2 tunnelling to L3 tunnelling. Possible border con- trol elements for security inspection are firewalls, filtering routers or IPsec end points. Packet filtering towards backbone and ISP/corporate, as well as downlink/uplink address screening, is found in GPRS edge nodes. When applied to a large company the main idea looks like Figure 6.14. Numbering - DNS Protection DNS is, as explain