Bind to 127.0.0.2

Question

I'm running a client/server application locally on my Windows XP PC and for testing purposes I want to run multiple clients.

The server has a configuration file containing the IP addresses of the clients that can connect; in the real world, these would all be on separate hosts with separate IP addresses.

Currently I am able to test locally with a single client which binds to 127.0.0.1 however because I can only have one client-IP mapping in the server configuration (that's how the system works and can't be redesigned!) I can only run one client on my development PC.

I've tried to start another client application bound to 127.0.0.2 connecting to the server which is bound to 0.0.0.0 however the server thinks that the client is connecting from 127.0.0.1 again and so rejects what it believes is a second connection from the first client.

Can anyone suggest a way to get around this problem? I believe I could run one more client bound to the external IP address of the PC but I'd really like to be able to run multiple.

I know I could use VirtualBox or similar to run new instances but I'd like all of the client applications to be running in the Visual Studio debugger.

Any help greatly appreciated!

Nick.

PS. Not sure if it matters but the applications are written in C++ using standard winsock sockets.

@Tomalak: Yeah I know that - I guess there's no way for the stack to work out which of the local addresses it's bound to :( — Nick, Mar 11 '11 at 10:43
@Nick: Your loopback interface is 127.0.0.1. If your application is bound to the loopback interface, it is bound to 127.0.0.1. not 127.0.0.2. — Lightness Races in Orbit, Mar 11 '11 at 10:46
@Tomalak: Yes, but I'm explicity binding the second client application to 127.0.0.2 - maybe I didn't make that clear. — Nick, Mar 11 '11 at 10:48
@Nick: No, you made that clear, but perhaps what I didn't make clear is that you're still binding to the loopback interface, and that has address 127.0.0.1 on your system. You can't get around that just by picking an arbitrary IP. — Lightness Races in Orbit, Mar 11 '11 at 11:13
Why don't you just add multiple ip addresses to your network adapter but on the same subnet? Or bind on different ports? — Derick Schoonbee, Mar 11 '11 at 12:36

score 2 · Accepted Answer · edited May 23 '17 at 09:58

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You might be able to create more loopback interfaces. See the chosen answer to How do you create a virtual network interface on Windows?

edited May 23 '17 at 09:58

Community

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answered Mar 14 '11 at 12:49

Ilkka

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score 1 · Answer 2 · answered Mar 14 '11 at 09:42

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AFAIK Windows 7 (maybe Vista too) lets you add multiple IP addresses to a single interface (card).

answered Mar 14 '11 at 09:42

vbence

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Bind to 127.0.0.2

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