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Keep Your Virtual Machines and Hosts Talking Without a TCP/IP Connection

You don't need to pay for a connection to the Net when you're working remotely. Loopback adapters enable a disconnected machine to have a working TCP/IP stack.

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.

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