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I am going to be setting up Windows Server 2008 for a small business (15-20 users). I will be getting a dedicated T1 for the server, being that it will be hosting email through exchange server.

Being that a T1 is too slow for 20 users, I am ordering a Cable/DSL line for my users.

How would I configure my setup so that DHCP is still hosted by the server, along with Active Directory, Exchange, etc. but the server uses ONLY the T1 for its internet connectivity, and the LAN users ONLY use the Cable/DSL line for internet connectivity.


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You will probably have two routers, one for each connection. Make the default gateway for the server be the internal address of the T1 router, and all the other machines will use the cable/dsl router's internal IP for their default gateway

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+1 mfinni - Note that using something like the cisco asa5505 or cisco asa5510 will allow you to do this with one router (there are other good options besides cisco) – Patrick R Feb 15 '10 at 21:58
I do exactly this scenario with 2 routers. Having the 2 routers also gives you a bit of hardware redundancy. Either router could temporarily take the place of the other. – Keith Stokes Feb 15 '10 at 22:47

Why not request a static IP address for your business?

Then you can do away with the T1 line altogether. Poke a hole in your DSL router to forward port 25 to your internal exchange server.

Set up the DNS mx records for your domain to point to your static ip address.

If you can't go static, then it may be possible to use the dyndns service. I don't have any experience with dyndns personally as we've always been able to get a static address.

Yes and to answer your question directly. You will only want one DHCP server on the LAN. Most routers have it built in. I'd disable them all. Put DHCP on the windows server. Set a static ip for the server and set it's default route in the network card to be the T1 line. In the DHCP server make sure that the default route is the DSL router ip address.. Make sure that you set your routers with internal ip's that will never conflict with what the dhcp server will give out...usually I just set dhcp server range to be from - or similar. Then set your routers to be numbered above 200.

The reason for using the windows dhcp server is because it interoprates with windows dns. Windows DNS is pretty vital for computers using active directory. A built in dhcp server doesn't do and support all of Microsoft's non-standard extensions.

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I think that the answer is to use different class-C networks for the two segments. Give the Exchange server one network - probably a public IP address, and give your users a private network.

Then, give the Exchange server an IP address on the private network; you may need to add an additional NIC to that server. Make sure that the exchange server has a gateway configured only for the public network. You can easily use Active Directory to act as a DHCP server for the private network, just make sure to turn off the DHCP service on your cable modem. Configure the DHCP service to issue the cable-modem's IP address as the gateway.

Your users will be able to retrieve their mail on your fast local network, but since your users are using the cable-modem's IP address as their gateway, all normal internet traffic will pass through the cable modem.

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Two different data feed for a small business may an overkill. Does the end-users job require them to actively use the web? If not a T1 is quite sufficient.

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