We have 5 internet ip starting from 72.x.X.63 to 72.x.x.66. 72.x.X.63 and 72.x.X.65 are already connected to a seperate router and both are linksys routers. i now connected 72.x.X.66 to a dlink router. Now the issue started, Machines connected to all the 3 routers are not able to access the internet. When i remove the DLINK router it starts working. My guesses are 1. Already available routers are linksys and new one is dlink. 2. Already available routers are VPN routers and the new one is not a VPN router. 3. firmware needs to be updated to the multiplexer which distributer 5 ips from a single cable.

I'd check the internal interface IP address on both routers before doing anything else. It's entirely possible you have an IP conflict due to both trying to use the same IP. The problem with your setup is you will use up two of your IP's on the routers, limiting the number of clients you can attach. The sensible way to do this is to use a private IP on the LAN side and not even use the IP's provided to you by your ISP on anything but the routers. I suspect you want to keep the two networks separate since the two machines are plugged into a router with a VPN. If this is the case, assign one IP (provided by your ISP) to the VPN router, use something like 192.168.0.0/24 for the clients plugged into it (LAN side). Then, give the other router an IP (not the same one of course) and use 192.168.1.0/24 for the clients plugged into that router on the LAN side. This gives you separate subnets and properly configured, will allow internet access to both subnets without conflict.

Thanks for ur help i have three routers each connected to a different internet ips. On which 2 is working perfectly before. The one which i added now disturbed the environment which was working perfectly before. To clear up ur thought internet | /|\ / | \ / | \ .63 .65 .66 .63 and .65 is the two subnet working fine before. .66 the new subnet which collapsed the the other two. When i unplug .66 subnet it again started working. Hope we will resolve this issue.

diagram internet<>switch [you call concentrator] then routers 1,2 and 3 correct? Are you doing a static ip assignment to router3? Or is the wan interface configured for dhcp? The cable you are using between dlink and switch works if connected between linksys and switch? When it stops working can you http into one of the linksys's? If so what does the router tell you is the problem? No connection, what? Technically there is no reason you can't have 5 routers connected to the switch with this config. Are you ready for where Microsoft wants you to go today?