Best way to merge 2 different networks/companies in same building

[david.santel]

I would like to get some thoughts on best practice regarding joining 2 different networks in the same building.  2 different companys 2 different networks, we are merging. Once networks are joined we will trust the windows domains.

Both networks are using 3750's for core switching. So i would assume running fiber from Company1 core to Company2 core via  trunking and sharing select vlans across the cores would be least expensive and most secure route?

Other ideas or flaws in the idea I have presented?

Thanks!

[James Leinweber]

Other than the usual subnet and routing issues, stringing trunk fiber between the switches sounds good.

If there are multiple firewalls and ISP's involved, you'll have to pay close attention to the routing topology, or reengineer to reduce the complexity.

If there is overlap in subnet usage, you might want to renumber one side.  Using NAT internally will be an ongoing maintenance headache.

-- Jim Leinweber, WI State Lab of Hygiene