How to combine two offices via the Internet into a single local network?

Question

VPN

There is such an idea: to combine 2 offices in different parts of the city with different providers into a single local network.
And since I am not an expert in this matter (“you understand computers, so figure it out”), then I tried to find an explanatory guide on the Internet, but I did not find it. Therefore, I ask for help here - write how it is done or give a link to the already described manual, please ...
Something like this:

LAN 1 - the central office. The Internet from the provider was connected via PPPTP to the TP-LINK WR743ND router, a static IP was received from the provider. Clients cling to a router on Wi-Fi (for the most part).
If I understand correctly, you need to raise the VPN to complete the task. Is it so? Can this be done on this router?

Answer 1

That's right, you need to raise VPN
But it won't work on your routers, because you are already using PPPTP. You need to either change the router, or put another piece of hardware behind the router and already raise VPN on it

Answer 2

It is possible on OpenWRT or its derivative DD-WRT
But I would use the classic static ipip or gre tunnels (if the addresses are white on both sides) or ipsec (tunnel)
On OpenWRT, if desired, and openvpn can be deployed

Answer 3

If I'm not mistaken, then DD-WRT can work in both client and VPN server mode at the same time, you can install this firmware on the TP-LINK WR743ND, on the second it's not clear what kind of router it is. If you can put on both, then you can configure everything directly on the routers, if not, see the advice above.

Answer 4

Tell me if 2 offices each have their own white ip. There are routers.