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multi building and firewall routing

I have two buildings connected with fiber and running multiple VLANs.  The VLANs extend to both buildings.  The default gateway is a 300e located in building 1.  We want to add a second firewall (301E) in building 2 with its own internet and set up routing between the two firewalls.


Objectives are 

1. each building sends internet traffic out its own firewall

2. if the fiber connection between the buildings is cut, the firewall will reconnect over a site to site link

3. Both buildings will continue using the same default VLAN (


Any thoughts on how to make this work?




Can you please tell me, what is the reason to have routing between the Fortigates and to have a requirement to use the same subnet in both buildings?

Is there any specific reason you would like to use the same subnet on both buildings?




had to extend a VMWare cluster between the buildings and just didn't have the timeframe to do anything except extend the VLAN across both buildings.  Now I need to figure out, how to route between two buildings, allow a VMware cluster to work on different subnets, make the best use of Internet access in each building, and finally make everything fault-tolerant.


I am thinking that I should move internal routing off of the FortiGate and back to the FlexFabric switches I have at the core.


Any recommendations?