Not able to connect to internet when ISP router connects to Cisco switch

Hi Guys,

​

We have a new ISP at our new building, the provider has a router at our rack, and we connect it to a port on our switch - we then give it "switchport access vlan XXX", we then connect our firewall which is a Fortinet, to port on the switch, and assign it the same vlan number as the vlan we assigned the ISP - i then configure the outside interface on the firewall with the provided public IP provided and set static route, but after that, I dont get internet traffic.

​

HOWEVER, when i connect the router straight to the fortinet firewall, and configure the outside interface, and static route, i get successful internet connectivity.

​

I'm not sure what else to look at on the switch, any idea guys?

​

The switch is a Catalyst 9407.

​

Thank you!