Using the Alternate Configuration Feature

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The Problem:
I was chatting with a consultant the other day, and he told me he was planning to upgrade his laptop from Windows 98 to Windows XP to gain the Alternate Configuration feature for TCP/IP settings. This feature lets a computer automatically switch to a second, alternate, configuration for TCP/IP when the primary configuration doesn't work. It's a nifty way to take a laptop to another site and connect to a network at that site.

The consultant's office runs SDSL, and each computer on the network has a fixed IP address. At his client sites, he runs Windows 2000 domains with DHCP services. He told me he'll set up his laptop's NIC with the assigned TCP/IP address, then use the Alternate Configuration tab to enable the option "Obtain an IP Address Automatically," which will let him connect to his clients' networks with an IP address that the DHCP server gives. My response was "Yep, that Alternate Configuration feature is really nifty. Lotsa luck, I'll be happy to help when your plan fails." Why did I say that?

The Solution:

The Alternate Configuration option is available only if the original TCP/IP configuration obtains an IP address automatically. In fact, if you configure TCP/IP for a static IP address, no Alternate Configuration tab is available.

The alternate configuration doesn’t kick in until a computer has searched for a DHCP server and failed (the system searches for about a full minute before deciding to give up). The system then looks for settings on the Alternate Configuration tab to determine whether to use APIPA for TCP/IP configuration, or to configure TCP/IP with the information stored in the alternate configuration.