mong other things, virtual machines are great for doing demos of software. But when a demo requires a TCP/IP connection and a network isn't available, you must make adjustments. When performing a demo at a client site, for instance, the client likely won't allow you to access their wired or wireless networks. With no physical network available, the host's network adapter lacks a TCP/IP stack and it simply won't function, as this IPCONFIG shows:
Windows IP Configuration
Ethernet adapter Local Area Connection:
Media State . . . . . . . . . . . : Media disconnected
Although public Wi-Fi hotspots and even some airplanes provide a network connection for a price, in many cases you don't need to pay for a connection to the Net. You just need a working TCP/IP stack to enable communication between your host and your virtual machine(s). Enter loopback adapters.
Loopback adapters, in both software and hardware, enable a disconnected machine to have a working TCP/IP stack. Software loopback adapters can provide special functionality when a network is not available and also when one is. Hardware loopback adapters, though often overlooked, offer convenience by offering loopback functionality without requiring you to reconfigure settings like a software loopback adapter does. A hardware adapter literally is plug and play. This article introduces both technologies and explains how and when to use them.
As a primer, here are definitions for the virtual machine terminology you will encounter in this article:
- A host is the physical machine on which Virtual PC or Virtual Server (or similar products such as Zen, Parallels, and VMware) is installed.
- A guest is a virtual machine running inside Virtual PC or Virtual Server.