OK here the situation, I work for a travel agency and we have 2 different network in our office. Lets name them network A and network B. Network A is our main network with runs in our entire office, meaning most of our pc's are connected to this network including windows server 2003 as an Active directory, its ip range is 172.29.12.0. Also have a ADSL router connected to the internet. So PC connected to the Net A can access internet easily.

Network B has a different IP range its starts with 172.16.128.0, there are only three PC in this network range, these PC are connected to a switch and a cisco router is also connected to this switch pc's, the router is connected to a leased line. These pc's run a reservation system directly connected to the router. The PC are just used for the this particular reservation system. They have windows xp running on them but they don't have internet connection.
Now my question is that can I share our internet connection on Network B without changing the IP address on network B. I want Network B to have internet as well as there reservation system running smoothly. Instead of giving them PC which will be connected to network A for the user to use internet.

Would appreciate if someone could help.

Yes you can do this. Do you have access to the Cisco router or is it managed by the Agency or ISP? Can you make changes to it?

First you must physically connect both networks together. Add a connection from switch to switch in each network.

In your notation, you show each network as a Class C even though the 172.16 to 172.31 ranges are typically Class B. I am providing the example below as if they were both 24-bit instead of 16-bit subnets.

Access to Cisco Router - yes:
Add a route to your Cisco router that includes the 172.29.12.0/24 network with the ADSL router as the gateway address. Add a route in the ADSL router for the 172.16.128.0/24 network with the Cisco router as the gateway address.

Access to Cisco Router - no:
Add a route in the ADSL router for the 172.16.128.0/24 network with the Cisco router as the gateway address. At a command prompt, add a persistent static route to each of the three PC's as follows (assuming that 172.29.12.1 is the ADSL router address):

ROUTE ADD -P 172.29.12.0 MASK 255.255.255.0 172.29.12.1

You are done. Each network must be aware of the other and must know what route to take as the exception for the default routes.

ok here the situation, i work for a travel agency and we have 2 different network in our office. Lets name them network A and network B. Network A is our main network with runs in our entire office, meaning most of our pc's are connected to this network including windows server 2003 as an Active directory, its ip range is 172.29.12.0. Also have a ADSL router connected to the internet. So pc connected to the Net A can access internet easily.

Network B has a different IP range its starts with 172.16.128.0, there are only three pc in this network range, these pc are connected to a switch and a cisco router is also connected to this switch pc's, the router is connected to a leased line. these pc's run a reservation system directly connected to the router. the pc are just used for the this particular reservation system. They have windows xp running on them but they dont have internet connection.
Now my question is that can i share our internet connection on Network B without changing the IP address on network B. I want Network B to have internet aswell as there reservation system running smoothly. Instead of giving them pc which will be connected to network A for the user to use internet.

would appreciate if someone could help.
Firstly thanks chuck for your help.
The Cisco 800 series router belongs to one of the Airlines, it's their property at our premises, they had configured it accordingly. It is accessible to me but I am not sure how to add a route to it. I could probably do it if someone could guide me.

I did try your second option, to add a route to my LINKSYS ADSL router. I manage to add a route in its WEB GUI. Then I connected both the network swtich together. I tried to add a route on the Network B PC but there was an error saying the "the route addition failed: either the interface index is wrong or the gateway do not lie on the same network as the interface, check the IP address table for the machine." In the command I had typed what you had asked me to "ROUTE ADD -P 172.29.12.0 MASK 255.255.255.0 172.29.12.1".

Chuck there is one more problem involved, In network A, we have a firewall box as well which is placed between the ADSL router and 3 com 24 port switch. Now this is box we got it from a company called VistaWiz, mainly we require for VPN connections on dynamic ip. It has a WEB based interface and has a firewall menu tab in it, but to be honest it's a bit complicated. The ADSL router and the firewall are bridged. If I ping the router within the network I get no reply but if I ping the firewall box it replies. There are ethernet ports on the ADSL router, should I just connect ADSL router directly to the Network B swtich. I have added a route in the ADSL router but then the route command on the Network B PC don't work.
Need your help. Thanks

Firstly thanks chuck for your help.
The Cisco 800 series router belongs to one of the Airlines, it's their property at our premises, they had configured it accordingly. It is accessible to me but I am not sure how to add a route to it. I could probably do it if someone could guide me.

I did try your second option, to add a route to my LINKSYS ADSL router. I manage to add a route in its WEB GUI. Then I connected both the network swtich together. I tried to add a route on the Network B PC but there was an error saying the "the route addition failed: either the interface index is wrong or the gateway do not lie on the same network as the interface, check the IP address table for the machine." In the command I had typed what you had asked me to "ROUTE ADD -P 172.29.12.0 MASK 255.255.255.0 172.29.12.1".

Chuck there is one more problem involved, In network A, we have a firewall box as well which is placed between the ADSL router and 3 com 24 port switch. Now this is box we got it from a company called VistaWiz, mainly we require for VPN connections on dynamic ip. It has a WEB based interface and has a firewall menu tab in it, but to be honest it's a bit complicated. The ADSL router and the firewall are bridged. If I ping the router within the network I get no reply but if I ping the firewall box it replies. There are ethernet ports on the ADSL router, should I just connect ADSL router directly to the Network B swtich. I have added a route in the ADSL router but then the route command on the Network B PC don't work.
Need your help. Thanks

I forgot to mention the fact that the PC's in network B have to have static IP addresses so that they can be assigned a second IP address. Sorry about that. And if you are handing out DHCP in the A network, you can not use DHCP in the B network once they are connected together. With only three PC's, I assumed you were not.

So, select three IP addresses outside of your DHCP scope on the A network and add one to each of the PC's in the B network. Go to the Advanced network properties in TCP/IP configuration and add a second IP address. This way, each of those three PC's will have an address in both networks with the primary address in the B network and the gateway address in the B network. DO NOT ADD A SECOND GATEWAY ADDRESS. This is what the static routes are used for. They add the gateway address for ONLY the A network usage.

Do not worry about the Firewall and not being able to ping the router. The Firewall is port blocking the ICMP response... in other words... no pinging. Trust me. The communications channel is there. The Firewall is doing what it is designed to do. Try and ping something like yahoo.com. You will get the IP address back which means that name resolution is being performed but the ping will not return any replies. This is to be expected.

Hi there chuckhole, I tried as instructed but still no result.
Firstly I added a route in the linksys ADSL router.
Then I added secondary ip addresses to the 3 pcs.
I didn't add the gateway but I added our DNS server address.
Confirmed with the route print and saw the route was persistent.
But still no internet though it pings to our firewall, to our DNS server, to all the pcs on network A but when I browse "the page cannot be displayed".
The reservation ticket system works perfectly fine.

I feel its something small now. Any help?

Does your DNS server have a Forwarder configured? If it does not then the Internet DNS requests from your 3 PC's will fall on "deaf ears".

Option 1: Go into your DNS server configuration and add your ISP DNS server addresses as Forwarder addresses to forward all requests not contained within your zone. This way, when your clients request an Internet address, it can forward the request on to your ISP's DNS servers for name resolution. The PC's in the other network will not require this because their normal route takes them out through your Internet gateway.

For Windows DNS, open the DNS MMC Snapin. Add the DNS Server to the list. Right-click on the DNS server name and select properties. There you will see the Forwarders configuration tab. Add your ISP DNS server IP addresses here.

Option 2: Configure your 3 PC's DNS server addresses to be that of your ISP. This is less desirable since they will not be able to perform name resolution on your internal network.

In either case, make sure that the TCP/IP configuration, Advanced settings, DNS suffix for the connection is the same DNS domain as all of your other computers. You want all of the PC's to be hosts within the same DNS domain. This is especially important if you choose Option 1.

When the 3 PC's in the second network attempt to perform name resolution, it will see that it needs to refer the question to your DNS server. However, it can not respond to this request. So where does it go from there? The DNS server needs to forward the request on to an authoritative DNS server that can answer this request... one from your ISP. It can perform name resolution via its primary route which is your reservation system. So the alternative pathway must be defined.