Hi,
I want to set up a small lab of 2 computers to practice for linux security,but i dont know which lab
would be better, lan or wan.By wan i mean i can afford to have 2 different isp connections on 2 computers.i m new to this and dont know much about how to form an infosec lab to practice for system security
and having 2 isp connection also sounds crazy so please
advice what can i do and what devices will i need.os is rhel4
thanks

It doesn't really matter. The only difference between a LAN and a WAN is, essentially, the price it will cost you to run one.

There is no difference if you are testing your system on a local network or over the Internet, as long as all of the security features of the server are configured to run on all interfaces of the machine.

Further more, since this is a test of security concepts, we can assume that the target machine you will be playing with will probably be setup with some exploitable weakness that you will examine from the other machine in an effort to better understand it. That being the case, such a machine should be isolated from the Internet anyway.

Thanks MS3FGX,I understood.

Another point of view is that some ISPs may not like it if you try to hack another computer trough their network, even if you owned both computers. It surely varies depending on your country and ISP, but I know in some places you can get into trouble if you happen to do something as "harmless" as portscans on your own machine over wan, not to mention anything bigger. It sounds funny but don't take the risk, if you can, use LAN instead; there you're isolated from the outside world, and the outside world is isolated from you.

It's probably a bit faster too, if you work on LAN, since the packets don't have to travel all the way to an external server and back. After all your machine doesn't really know about "internet", all it knows is that some data comes in from a device (for example eth0) and some data is sent to the device; everything behind the device is usually completely unknown to your machine (all it needs is the place where the data comes and goes and what to do with it, the source isn't important itself).

If you're practicing security, or breaking it, then for the purpose of understanding certain attacks you may want to deliberately introduce specific vulnerabilities and lax security on the target host. So I'd go for the safe option, meaning LAN-side.