Why does Fortigate require me to make LACP configurations separate networks?

[khuffmanjr]

Hi!  First post.

I recently got into a Fortigate 40f and then quickly upgraded to a 60f (not a waste; I have another use coming up for the 40f).  I have the Fortigate connected to multiple WANs (in SD-WAN), PC, TV/chromecast and a WAP.  I'm also connected to a distant home office where I plan to have a cisco stack of two switches with some other PC/Server devices, TV/chromecast, another WAP and some IoT (wireless bulbs and cameras).  I plan to LACP the cisco stack back to the Fortigate.  I want everything on the same network and, in the future, I plan to move the WAPs and IoT off to a separate vlan.

My question is this:  Why must I make the LACP connection to my cisco stack a separate network on the fortigate?  This is essentially just etherchannelling "two" switches together - the Fortigate hardware switch and the cisco stack.  Is there a way to have all Fortigate LAN and Fortilink ports on the same hardware switch and still use LACP to connect my cisco stack such that everything is on the same LAN segment?

Thanks!

[gfleming]

You've lost me at "placing a third switch in the stack at the FGT".... not sure what you mean here.

But in any event, yes if you are using LACP to connect FGT to your switches, everything on the other FGT ports will have to be routed over the LACP to the rest of your network (unless you use a software switch).

The other alternative here is that you put all your L3 VLAN interfaces on the FGT and just have a LACP trunk port connecting downstream to your stack. The FGT is a very high performance router so this would work nicely.

[khuffmanjr]

Ok, thanks.  Yeah I was just referring to my physical layout originally described.  I have two places to network together about 80ft apart.  The FGT and my two WAN connections are in one room with a WAP, PC and TV/Chromecast and the other room (80ft away) has more PC/servers, WAP and TV.  I had originally wanted a two-switch stack in the second room and for everything to be on a flat network between the stack and FGT LAN (expecially the WAPs).  I'm thinking now to extend the stack to three switches with two in the second room and one in the room with my FGT.  Then everything can just be on the switch stack.