There are many objectives covered on exam 70-272 Supporting Users and Troubleshooting Desktop Applications on a Microsoft Windows XP Operating System. You can view all the objectives on the Microsoft Learning Web site.

Although not explicitly stated, you do need to understand a bit about IP addressing, especially when it comes to troubleshooting. Some of the things you need to understand include:

  • IP address lease process (doesn’t hurt to understand how your computer gets an IP address
  • Configuring TCP/IP in Windows XP
  • Troubleshoot TCP/IP addressing

So, before you jump into learning about configuring IP addressing, here is an overview of what happens when a DHCP client requests an IP address from a DHCP server.

The process of leasing an IP address occurs in the following four phases:

  1. Discovery – The DHCP client broadcasts a DHCP discover message on the network containing its MAC address and NetBIOS name. If no DHCP servers respond to the request, the client continues to broadcast up to 4 times at 2, 4, 8, and 16 seconds. If a response is not received during this time, the client continues to broadcast every 5 minutes.
  2. Offer – Each DHCP server on the network that receives the request responds with a DHCP offer message. An offered IP address is included in the message.
  3. Request – If multiple DHCP servers respond, the client selects the first offer it receives and broadcasts a DHCP request for the IP address. The message is broadcast on the network because the client has not yet been assigned an IP address; it has only been offered one.
  4. Acknowledge – The DHCP server responds with a DHCPACK (acknowledgment) granting the client’s request to use the IP address. The DHCPACK also contains information about any DHCP options that have been configured on the server (such as the IP address of the DNS server).

Now another point to keep in mind here is that if a DHCP server does not respond to a DHCP client’s request for an IP address, Automatic Private IP Addressing (APIPA) may be used. The DHCP client will assign itself an IP address in the range of 169.254.0.0 to 169.254.255.255. The client can communicate on the network, but only with other clients on the same subnet that also are using an IP address in this range. If clients are running Windows XP, you can use the Alternate Configuration tab from the Internet Protocol (TCP/IP) window to manually configure the automatically assigned IP address and other parameters that should be used if the DHCP server is unavailable.

[tags]exam, 70-272, DHCP, XP, IP addressing, troubleshoot[/tags]