Could someone please help with a network problem?

billynomates

New Member
Hi

Wondering if you can help - this has got me (and most of my workmates!) totally stumped!

I use Vista 32 bit as a central machine on my network. This comprises a set of (old!) VMS/Unix machines, with static IP addresses, on a 192.168.1 subnet and a set of DHCP'd (mainly Windows) machines on my 192.168.0 subnet.

A diagram is enclosed...

The Vista machine is on both networks, and has IPRouterEnabled set to '1' in the registry.

I can connect to both networks on the Vista machine with no issues.

How on earth do I connect from, say, 192.168.1.2 to the internet (e.g., for Unix O/S updates)? Or from one of the DHCP'd windows machines (e.g., 192.168.0.3) to say, 192.168.1.4?

I guess this is something to do with routing, but I just haven't got a clue when it comes to this sort of thing...

Any help would be very much appreciated...

Many thanks.
 

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Think of it from the point of view of where a particular packet is going. Example:

1) The DHCP client whose IP is currently 192.168.0.2 wants to send a packet to the Solaris host at 192.168.1.3. It knows the destination IP, but it has absolutely no idea where the 192.168.1.X network is located. All it knows about is its own subnet - 192.168.0.Y, as well as its default dateway (DG) which is the wireless router at 192.168.0.254. The function of a DG is to serve as the last resort, so our hapless client forwards the packet destined to the solaris host to the DG... and that has absolutely no idea where the 192.168.1.X network is located either, so it attempts to forward to its own DG upstream on the internet... and the first "real" ISP router that gets the packet will unceremoniously drop it because it's destined for a "private" range that shouldn't be floating about the Internet.

2) Now you're the UX host and you're trying to get to something specific on the Internet, perhaps an IBM web server at (say) 9.10.20.30. Since the UX host has no specific route for the A-class 9.r.s.t network, it forwards the packet to its default gateway - 192.168.1.1 - the Vista PC - which will in turn probably forward to its own DG, the wireless router, and so on to the IBM web server. The response then comes back to the wireless router, which looks up its NAT session mapping and notices that the original requestor was "192.168.1.2", and it promptly goes into a nosedive because it has no idea where the 192.168.1.Y network is to be found, as covered previously.

What you have yourself there is a classic "Welcome To IP Routing 101" exam question :)

My first inclination would be to suggest that you remove the Vista box acting as a router, and to instead uplink the hub with the UX/Solaris/VMS hosts directly to a wired port on the router - they all have at least one port. If it's got several ports, you can even bypass the hub and use a different port for each wired connection. That "flattens out" your network so that every machine is on the same 192.168.0.X range, and they use the wireless router as the DG, and you don't really have anything else to worry about.

Otherwise, if you actually have to persist with this setup for some reason, you'll need to add some persistant routes. For example, on each of the 0.X machines:

ROUTE ADD -P 192.168.1.0 MASK 255.255.255.0 192.168.0.1

In other words, add a persistent (-p) route that sends all packets destined to the 192.168.1.Y network to the external interface of the Vista box. Since it straddles both networks (it has an interface on each one), the Vista box alone needs no modifications, most likely.

You'll also want to "teach" the NIX hosts where to find the 192.168.0.X network, but their admins will be good at those commands already, haaar :)
 

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I see. Luckily for you, the same ROUTE command is also used on Unix, although the syntax is a tad different. If you type MAN ROUTE you'll see the manual page.
 

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