We have an office that has their own independent network and ISP provider in the same building where we provide network access to our remote offices. They need to access our intranet. We are thinking of running a cable from our switch to their office.
The key question is, how do we make this work?
They have a Windows server hosting an Active Directory domain, single forest, single subnet 192.168.18.0. AD DNS, WINS and DHCP, Terminal Services is running on the server. The internal network communicates with outside world via a single firewall gateway, a Sonicwall TZ170 I believe.
Physically, all CAT5 cables are connected to a 16 port unmanaged switch which seats right on top of the server and links to the Sonicwall device. The Sonicwall device connects to an AT&T DSL network.
The network used to have a Gateway to Gateway VPN tunnel that links to another office in a different city, but it has been recently taken out as they have deployed Exchange Server at their site. Currently, the Sonicwall is being used as a gateway for Client base VPN access.