Lesson 2 in .NET framework

Maker Code 128 in .NET framework Lesson 2

Troubleshooting Internet Connectivity 12-23

Important In general, a client machine should be pointing at one of your internal DNS servers rather than using your ISP DNS server settings.

If you suspect DNS name resolution issues for your internal servers, you should next run the Nslookup command from the client system. Nslookup can help you determine whether your client is getting the right records returned from the DNS server you have told it to use.

If you suspect DNS name resolution issues for names beyond the scope of this partic ular server, or if name resolution issues exist for names outside your company, you should next check the DNS server itself. First, make sure the DNS server is forwarding to the next logical place based on your network design. You perform this task by ver ifying the Forwarders tab, as shown in Figure 12-18.

Figure 12-18

Typically, the DNS server forwards to a server with more knowledge of the network layout, or directly to the ISP itself. If this is not the case, you need to adjust the settings on the Forwarders tab. Additionally, verify that the server itself is responding to requests and that it can also respond to tests on servers to which it forwards information. In the example shown in Figure 12-19, the server itself is responding to resolution requests; however, it is unable to get any resolution from servers to which it forwards.

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Figure 12-19

This failure could indicate that the name resolution is not on your servers, but rather on servers on which your servers rely.

If you inspect the client computer and you receive unexpected settings in the network adapter, there could be many possible causes. If the client is expected to use Dynamic Host Configuration Protocol (DHCP), you need to ensure that the network adapter is correctly receiving the DHCP information. If you discover that the IP address of the client machine is in the range 169.254.0.0 through 169.254.255.255, you are using Automatic Private IP Addressing (APIPA). Therefore, your client is not receiving DHCP information from the DHCP server.

You can perform many steps in one step by using a new Windows Server 2003 feature inside the graphical user interface (GUI) the network Repair feature. You can find this feature while inspecting the status of a network adapter, as shown in Figure 12-20.

Troubleshooting Internet Connectivity 12-25

Figure 12-20

Clicking the Repair button initiates many actions as if they were each typed on the command line. The commands are performed in the order listed in Table 12-2.

Table 12-2

on the Command Line Ipconfig /renew Arp d * Nbtstat R Nbtstat RR Ipconfig /flushdns Ipconfig /registerdns

Attempts to renew the DHCP lease Flushes the Address Resolution Protocol (ARP) cache Reloads the NetBIOS cache Sends the NetBIOS computer name to Windows Internet Name Service (WINS) for an update Flushes the DNS cache Registers the name with the DNS server

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If the client computer is not receiving an IP address and at least a primary DNS server address, the client will certainly not be able to find the Internet. The following are some reasons the DHCP information might not be delivered to the client:

A router is blocking the Boot Protocol (BOOTP).

Furthermore, while you are inspecting the DHCP server, you might also verify that the address range it is distributing is OK, that the gateway is valid, and that the DNS servers point to a location that makes sense for your organization. You might also encounter a situation in which some clients can connect to the Internet and others cannot. After inspecting the clients networking characteristics, you discover that some machines are configured differently from others. However, all client comput ers are configured for DHCP. In this case, you might have what is known as a rogue DHCP server that is, a DHCP server that is set up in an ad-hoc fashion, perhaps for testing purposes. If this is the case, this server is likely providing the target clients with incorrect information namely, the gateway, DNS server address, or both. Microsoft Windows 2000 and Windows Server 2003 servers running DHCP must be authorized in the Active Directory directory service in order to serve as DHCP servers. If they are not, they automatically shut down. Use Dhcploc.exe, which is found in the Windows Server 2003 Support Tools, to discover DHCP servers that should not be authorized or other DHCP servers that do not need to be authorized, such as older Microsoft DHCP servers or non-Microsoft DHCP servers.