At what point should I configure Firewall on the network?

Question

Computer networks

Hello.
Please tell me at what points it makes sense to configure the firewall, and at what vice versa - turn everything off (or configure it somehow differently) - the network consists of the following:
1) USB modem Huawei E3372 (lte)
2) Mikrotik as a gateway ( a USB modem is plugged into it)
3) Mikrotik as a DHCP server (this one is in a different place, it’s necessary)
4) Other Mikrotiks (access points, switches, users)
I'm confused - where exactly what needs to be configured in terms of security ...

Answer 1

Firewall on the gateway to protect against external threats
On switches - vlan isolation at least
On the root router - vlan filtering and routing