OT: NAT Question

[Judas]

I recently had a quite long conversation with EDIT: Glyphon -> Gryphon about NAT router settings.

The basic setup is as follows.

Home LAN with 2 or more pc's

ip pc 1: 192.168.1.100
ip pc 2: 192.168.1.200

ip router internal: 192.168.1.1
ip router external: 217.xxx.xxx.xxx (real internet ip)

Default gateway is 192.168.1.1 and the router is running NAT.

Now assuming that on pc2 there is a TS server and a webserver running. You are on pc1 and can connect to the TS as well as to the webserver using the internal ip of pc2. You also have configured the router to foreward the corresponding ports to pc2 and everyone on the internet is able to connect to your servers.
Now you try to connect (from pc1) on the external ip of the router.

My experience is that this does never work. Yet Glyphon says it does work on any system.

Could someone with good knowledge of NAT, routers and networks please tell me now and forever if it works, and if so, how to do it, because i never ever have seen a system which allows connections on the external ip of the router from a LAN computer in the same subnet.

Thanks a lot

Judas

[Gryphon]

"Gryphon" ;)

In my experience, I believe this is true for "most" systems.

[N. Werensteijn]

Sorry. I get that to work on my linux nat box. :)

Well i guess it all depends on your hardware/software. NAT is not a official standard.

[Judas]

OK... having asked around quite some more it seems that all people unable to get it working are using either ADSL or SDSL hardware routers. The brand doesnt seem to matter as the same problem turns up on Zyxel, Lucent and a few other routers.

Having a LMHOST file which resolves the external to the internal IP makes accessing possible. Yet when pinging the external IP, it never shows up. All you see is the internal IP.

Maybe it has something to do with DHCP as well since none of the systems that have the problem use DHCP.

And last but not least it might be that software routers work differently. IE a software router might resolve the external IP to the internal with the first step whereas the hardware router (at least the ones that have this problem) doesnt have this lookup table an is unable to resolve an internal request on itself because it only can process external NAT requests?

Probably most "simple" hardware routers just lack the features a common linux software router has. I am wildly speculating now but it could have something to do with common ADSL routers only having a 1:n implementation of NAT whereas software routers usually support m:n NAT.

However, it looks as the problem could be narrowed down. Maybe there is someone out there who can tell me if what I was just assuming (especially the 1:n, m:n NAT part) is correct or complet bullshit ;)

Thanks anyway

Judas