Re: [Ethereal-users] Loopback adapter under windows

[Guy Harris <gharris@xxxxxxxxx>]

On Tue, Oct 29, 2002 at 06:45:31PM -0500, Adrian Sampaleanu wrote:
> The chart showing supported capture media says that Windows does not
> have a loopback adapter.  This is no longer true, I guess, since, at
> least under Win2K, you can install a Microsoft Loopback adapter.

The chart currently doesn't make it clear what is meant by a "loopback
adapter", so it doesn't make it clear that the Microsoft Loopback
Adapter isn't the type of loopback adapter to which it's referring.

"Loopback adapter", in that table, refers to an interface that is a
standard part of the OS's networking code and that *by default* handles
network traffic from a process on the machine to another process on the
same machine.

The UNIX loopback adapters are that type of adapter.

The Microsoft Loopback Adapter isn't, as it's an optional interface you
can install, not a standard part of the OS, and, even *without* that
adapter installed, you can send IP packets from the machine to its own
IP address, or to 127.0.0.1 (the loopback address), and have them be
received by the machine (at least I was able, on my NT 4.0 partition, to
ping the machine's own IP address, and 127.0.0.1, and get responses).

On Windows, there does *not* appear to be a standard loopback adapter
used for those purposes; I assume that the purpose of the Microsoft
Loopback Adapter is to deal with cases where you *do* want a network
adapter for testing purposes (so that what I presume is internal
looping-back by the networking stack isn't sufficient), or where you
need a network address other than one that belongs to a real network
adapter and other than the 127.0.0.1 (or other loopback network)
address.

I will update the FAQ to make this clear.

> Question is, though, is it useable by Ethereal - doesn't seem to be by
> my attempts

It would be usable by Ethereal only if it's usable by WinPcap, as
Ethereal uses WinPcap to do packet capture on Windows, and inherits its
capture capabilities and limitations from WinPcap.

> - and if not what is the technical issue stopping it from being used?

If it doesn't work with WinPcap, you would have to ask the WinPcap
developers what the problem is:

	http://winpcap.polito.it/contact.htm