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I'm on Windows XP SP3 and basically my topology consists of 3 computers (see drawing for more detail), a wireless connection to the Internet and a wired connection to a router. My main computer (A) is connected to the Internet (I) using a wireless USB card and the main computer is also connected to a router (R). The other two computers (B and C) are also connected to the router and the router itself is not connected to the Internet. I just want to use the router to connect the three machines together (a LAN) in order to send TCP packets (using BOOST-ASIO) from the main computer to either of the other two machines (which by the way are not connected to anything but the router that also connects to the main computer).

Network topology drawing:

A - Main computer with two connections I and R. This machine needs a subnet mask fix.

B - Computer connected to computer A through router R.

C - Computer connected to computer A through router R.

R - Router.

I - Internet.

 I    R------ 
 \   / \     \
  \ /   \     \
   A     B     C

The trouble I'm having is that I tried this setup already but I need to setup the subnet address on Windows XP somehow (I did search the Internet but nothing specific came up just the theory of subnet masking). My setup basically chooses the connection under the network connections->advanced settings-> network bindings and I cannot get both my LAN and Internet to work together?

They don't seem to explain the details on Toms Hardware either =(.

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Point of terminology: Although the router physically connects the computers, a computer can actually talk directly to other devices on the same subnet (essentially, you can think of it as a smart broadcast system). The difference is that the router doesn't perform IP-level tasks; it just acts as a switch, and doesn't need, say, an IP address for this to work. –  cpast Feb 25 '13 at 0:14
    
Also - Great description of your setup. +1 –  cpast Feb 25 '13 at 0:18

2 Answers 2

up vote 2 down vote accepted

You have two networks, one consisting of A and whatever connects you to the internet, and one between A, B and C. The "internet" network should configure automatically using DHCP. The second network may also have DHCP, perhaps conflicting. If it is conflicting, disable it in the router.

Then assign the following static IP settings to the PCs:

A - IP 192.168.123.10, Subnet mask 255.255.255.0
B - IP 192.168.123.11, Subnet mask 255.255.255.0
C - IP 192.168.123.12, Subnet mask 255.255.255.0

You configure this on the ethernet adapter. Leave the default gateway empty.

PC A has a second network interface, the wireless stick. Let that configure itself.

You are using the router as a switch. Make sure you do not connect one of the PCs to a "modem" or uplink port.

This assumes that you do not want to allow the other PCs access to the internet. If you do want that, you need to either bridge the WiFi to the Ethernet on PC A or make PC A act as a router. No matter which way you choose, your router still acts as a switch.

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Works now. I disabled DHCP on the router and used ip 172.16.1.1 subn et255.255.255.0 for the router LAN ip since my wireless ethernet card is 192.168.1.1. I then changed my router ethernet connection to 172.16.1.# subnet 255.255.255.0 where # is a number between 2 and 255, different for each machine connected to the router itself. The Wireless ethernet was untouched, settings were left on auto ip detection. –  lost_with_coding Feb 25 '13 at 1:36

Are you using DHCP ?

The solution would seem to me to ensure your wired interfaces are not using DHCP, and manually assign them IP's in the same subnet (eg 172.16.1.x) - You would leave the gateway empty (or use that of the router) and you should be able to specify a netmask of 255.255.255.0

(There are a number of sites which tell you how to set this up - just Google xp static IP - but I suspect your problem is you are using DHCP, so the subnet is left to the router to decide).

Note that I've recommended 172.16.1.x - you could, of-course, use anything in the range 192.168.x.x, 10.x.x.x or 172.16-31.x.x provided that it does not conflict with your Wireless connection.

BTW, Your explanation was very clear on your setup. Well done.

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