Can anybody help me to access Internet with my existing network

Question

Dear All Recently I purchased new WRT 54G wireless router. Also I have tied up with new ISP to give wireless internet access to some of the my Higher authority employees only. My office network setup is as shown below Local Ip range : 172.18.0.0 to 172.18.2.254 subnet mask : 255.255.0.0 Default gateway : 172.18.0.50 Wireless Router configured as : 1) configured all ISP settings 2) configured LAN site setting( But I had to setup lan as 192.160.1.X i.e the required by ISP ). 3) connected ISP lan port of WRT54G to cable coming from ISP Modem 4) Connected Local port( any one of 4 ports) to my existing switch(existing LAN----172.18.x.x network) Now suppose I configure user laptop to access new ISP internet through wireless.I have done following setting Wireless LAN setting : Ip address : 192.168.1.2( I can give any IP of network 192.168.1.x) subnet mask:255.255.255.0 Default gateway :192.168.1.1 DNS : Automatic I can access the new ISP internet without any problem with WRT54g router. But the problem is while accessing the new ISP internet( Using 192.168.1.x/255.255.255.0/192.168.1.1 network),Also I want to access my existing network( 172.18.0.0/255.255.0.0/172.18.0.50). Since I am very weak in routing the network, can anybody help me out to do routing setting in linksys WRT54g router so as to access my New ISP internet using existing network( 172.18.0.0/255.255.0.0/172.18.0.50). Please help me anybody

Answer 1

O.K. Still the crucial question remains whether you want the separation of the ISPs enforced or not, i.e. do you actively want to prevent someone to switch to the other ISP simply by reconfiguring some settings on the computer or not?
If you don't want to enforce the policy and it is enough to just use different IP settings on different computers then this would probably be the easiest solution.
If you can, install a DHCP server (e.g. on a Linux box) inside your network which does the DHCP address assignments. That way you can dynamically assign the proper addresses to the computers.
You can then assign the WRT an LAN IP address inside the 172.18 subnet. The DHCP server assigns anyone addresses inside your 172.18 subnet. However, you configure different gateway and dns server addresses depending on the computer. You configure the MAC addresses of those 'preferred' laptops the gateway address of the WRT and the public DNS servers of the new ISP. All other computers you assign the old gateway address of the old router and the DNS server addresses of the first ISP.
If you don't want to install your own DHCP server you can assign either pool static IP addresses, i.e. assign all preferred laptops static IP address including the gateway address of WRT and use DHCP only for the normal computers or vice versa.
What won't work reliably is to run two DHCP servers on both routers and connect the LAN of both together. You'll end up with computers picking up the wrong IP address from the wrong DHCP server.
Again, this separation only happens due to the different configuration of the computers. If anyone can freely reconfigure the computer he has it is easily possible to change the gateway address and thus swap the ISP. But as long as people comply with the rules it works.
If you want to enforce the separation you will have to install another router between the two gateway router. This third router passes traffic from the WRT subnet for the 172.18 subnet and accepts the return traffic. In the opposite direction the router does not forward traffic. You should even be able to use a standard NAT gateway router and hook up the internet port to the 172.18 subnet and the LAN port to the WRT. You then configure a static route on the WRT to forward packets for 172.18 subnet to the third router. If the third router does not NAT then you have to configure another route on the first router to forward traffic for WRT subnet (192.168.1.*) to the third router as well.