How to combine two offices with different providers into one local network via cable?

Question

Computer networks

We have:
Two offices physically located not far from each other and connected to one local network via optics.
At the first office, the Internet comes to Mikrotik, which feeds both offices with the Internet.
We do: We
connect the second office to other provider. We feed the second office, respectively, from the second provider, and the first office from the first provider.
Task:
It is necessary to combine two offices into one local network so that in the absence of any Internet provider, communication over the local network between offices is not lost.

Answer 1

There are two options.
1. Configure DHCP so that it issues different default gateways to the first and second offices.
The first - ip Mikrotik, the second - from the device that will issue independent Internet to the second office.
2. Separate office1 and office2 into different subnets, configure routing between them through optics, separate DHCP servers will accordingly issue their default gateway, looking at their routers on the Internet.

Answer 2

1. We set up a simple scheme when each office works with its own provider.
2. We teach Mikrotiks to go to the Internet through the "neighbor" when your catal falls

Answer 3

Divide by 2 networks, for example 192.168.0.0/24 and 192.168.1.0/24.
In office2, put a second router, Internet and optics from office1 into it, dhcp up on the office2 router.
In office1, you also transfer the optics to the router, raise some kind of grid like 10.0.0.0/30 between them and prescribe routes between the routers.
If a firewall is configured - allow access between networks

Answer 4

it at you one broadcast domain? and a mask like /22 or /8?
why use DHCP? high turnover in the network?
it is necessary to scatter everything with vlans to one common directory ... on a microte, raise redundancy and install a UPS