Two company networks in the same space

We have the need to setup an additional subnet in our office that will have a separate internet connection and gateway. This new network also needs to communicate with the existing network in the same office space. Two companies working in the same physical space with two separate internet providers and paths to the internet need to work with one another. I originally thought we may have to setup a VPN tunnel between the two, but then thought it may be possible with a layer 3 switch or routers.  Exiting network is new network will probably be
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Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
A L3 Switch or Router should work. The routers providing the internet connection should be able to interconnect the office networks, but they will need one additional address from each other network range for that purpose.
wlamoreAuthor Commented:
Are you saying that I may not need the layer 3 switch or an additional router other than the two internet routers that will be in place for the two networks to connect to the internet?
Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
If you are able to connect those two Internet routers - yes.

Some routers have more than the necessary two interfaces, and if you have a spare one, you can use that to connect the routers directly, using a different IP subnet used only for transfer between the other networks. That would keep the traffic separated from each other.

If you do not have the additional interfaces available, you just give the routers one IP address from the other network, and connect the LANs by a conventional switch. That will not separate traffic (much), and add some LAN overhead, since packets are sent more than once when crossing the LANs.

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