Merging two companies: Best practice?

Situation: Company A purchased Company B. Offices are 40 miles apart. There are about 10 employees in each office. We want to have everyone be able to access all network resources independent of location.

Company A - Windows 2008 Server domain controllers, Win XP, and Windows 7 workstations. Company B - Windows 2003 Server domain controllers, Win XP, and Windows 7 workstations.

Company A, has T1 connection to internet, and Cisco ASA 5505 firewall. Will add 2nd T1 line shortly. Company B, has 25x3Mbs connection to internet, and WatchGuard firewall.

Company A and B have different subnet addresses on their internal LAN.

How should this be done?

Solution 1:

Make a VPN connection between the two networks (site-to-site link between the ASA and the Watchguard.)

Configure a two-way-trust between the domains - this will probably entail some DNS changes. Then, start assigning permissions appropriately.

That will link the two networks and allow them to share resource.

Longer-term, you may want to migrate everything out of one domain into the other, but a good easy start is a trust. You will also want to move all of their processes into your framework and tools - AV, software licensing, monitoring, backups, etc. Infrastructure processes like that are best to consolidate, not run with two different systems.

Which brings up a good point - It may be a good idea to first do an audit of the new network to make sure the AV is up-to-date and there is no malware on the machines, before you make the VPN link.