Consolidation of local networks?

Question

Computer networks

Hey habr!
Situation: there are 7 offices in the city. Provider A is represented in all offices. It is
necessary to combine networks. The association should be transparent to users. Up to 5 people in 6 offices, 20 in 7 offices.
Which routers should be used? The best way, as I understand it, is to use GRE, right?
I would like to see two options, from cisco and, say, d-links.
PS Combine at the provider level (v-lan's, for example) is not an option.

Answer 1

What are you expecting from us? Spec, technical project and system architecture? It's not a Q&A question, brother, it's a job that costs money, that, apparently, was assigned to you (and paid, in the form of a salary or fee), and you want it to be done for you for free?
You will be answered for free the question “what to do vpn on, brothers?” - "on boobs, use IPsec or just GRE if encryption is not required."

Answer 2

mikrotik rb750g in a large office, rb450g is suitable for small ones.

Answer 3

We solved this problem first by uniting the provider, uniting all offices into one vlan. Then, having one vlan from the provider, it was subnetted. Then we switched to vpn to the vpn server, it is also a router, it is also a firewall, in the central office.
But our decision is specific, connected with fz No. 152. APKSh Continent - a piece of iron in the central office. Continent AP clients at their workplaces. In the second largest office, they installed another model of the Continent, they are able to raise the tunnel between themselves with almost no settings.
I will not say that this is the best \ convenient, etc. solution. And certainly not cheap. But certified.