You can prevent cache pollution on a Windows Server 2003 DNS server by using only secure dynamic updates and by activating the Secure Cache Against Pollution option that you select on the Advanced tab in the DNS server s Properties dialog box. The DNS server cache is sometimes a target for Internet attackers, who attempt to pollute its contents using unauthorized dynamic updates. If a DNS server has outdated or incorrect information in its cache, it might supply the wrong IP address to a client requesting the resolution of a particular Internet server name. DNS servers are also subject to problems caused by incorrect cache information. An incorrect Domain Name Service (DNS) server address (or a malfunc= tioning DNS server) can prevent a client from resolving Internet server names, therefore preventing it from accessing the server by using its name. An incorrect default gateway address prevents the computer from accessing resources on other networks (including the Internet) but does not prevent the computer from accessing the local network. Client connectivity problems can be caused by hardware, such as a disconnected cable or a malfunctioning network interface adapter, but the most common cause of Internet connection failures in a single client is incorrect configuration. Depending on whether you can recreate the problem on computers connected to the same hub, to the same LAN, to different LANs, or throughout the enterprise, you can isolate the problem as being located in the client computer, in a hub, in a router, or in the Internet connection itself. Determining the scope of an Internet connectivity problem is generally a matter of try= ing to recreate the problem on different computers. In many cases, the problem might be beyond your control, and the only solution is to call your ISP or the carrier that provides the connection to your ISP. To troubleshoot Internet connectivity problems, the first task is to iso= late the exact location of the fault and determine how many users are affected. When network users are unable to access Internet resources through a shared connec= tion, the cause of the problem can lie anywhere between the client computer and the Internet server.