The structure of the provider network?

Question

Computer networks

Hello! Please tell me about one question, perhaps quite trivial, but which has been tormenting me for quite a long time, but there is no answer)
I work as a helpdesk in one rather large company with branches in many large cities of the region, headquartered in Moscow. I believe that I know quite well how to build an internal network. My question is about the "external" network.
What we have: each branch is connected by a vpn connection to the head office (star topology), and all network processes between them go through the main office. Each office has a provider, Rostelecom, whose equipment includes a switch and a router. The router distributes a network like 10.1.xx.xx. On each crypto gateway on which the vpn connection is actually created, let's say ip 10.1.xx.254/24. where xx is the conditional code of each branch. Thus all vpn'itsya by "gray" addresses.
My question is about building a provider's network - how is its network configured, that two gray addresses on the gateways see each other? The distance between the head and branches can reach several tens of kilometers.
Please help, explain, etc. I would be grateful for any useful information!

Answer 1

Rostelecom can do it in different ways, but basically a separate VLAN is allocated for the subscriber and is passed through the network from port to port.
Rotelecom also has an SBA network (a network of business subscribers), there is L2 + (VPLS, MPLS, that's all).