ed earlier in this chapter, a very vital part of an IP network. DNS Security sees to it that the client gets an answer from the correct DNS server, that the answer is related to the query and that no changes have been made to the answer by an intruder. Understanding Changing Telecommunications - Building a Successful Telecom Business Department Department Internet Firewalls Corporate backbone Firewalls Department Department Figure 6.14 Network partitioning into zones Security Needs and Solutions for the Business Sector For economical reasons the protection level is different between different services. Ser- vices with the highest security requirements are e-commerce and computer networking, such as remote access, LAN interconnect, extranets between enterprises and links between enterprises and application service providers. Ultimately, Internet VPNs will be the global means of business communication just as the voice network is today. Casual e-mail is considered less risky, but at least business e-mail should be protected. Voice over IP may introduce risks for other services and needs protection against leavesdropping/wiretapping. In today's workplace there is a need to provide access to employees even when they are outside the office. This need arises first for the 'road-warrior' employees such as a sales persons or installation teams, but also for accommodating home workers and 'day- extenders'. Traditionally, such access has been provided with dial-in connections to a corporate network access server (NAS). See for example Figures 6.15 and 6.16. This approach has, however, several drawbacks: The corporation has to invest in the installation and management of the NAS. While easy and inexpensive from the same geographical area as the corporate offices dial-in access from overseas locations may be prohibitively expensive. The introduction of new access technologies such as digital subscriber line (DSL or xDSL, such as ADSL) with higher bandwidth but shorter distances is making the corporate-owned NAS approach no l