How to combine three networks using VPN on cisco?

Question

VPN

I understand with the help of Cisco Packet Tracer.
Actually there are three networks (and three routers, respectively), you need to combine them using a VPN. Either that network B and C have access to network A and vice versa, or that all networks have access to each other. Which is easier.
I found a very good instruction for combining two networks:

But I don’t understand well what needs to be corrected and added in order to set up a VPN between all three networks.

Answer 1

On the picture - instructions for setting up IPSec. First phase: 3DES encryption, MD5 hashing and peer address. Second phase: similar.
Then it is indicated from which networks you can hack, the settings of the cryptomap and the binding of encryption to the interface.
I don’t see where the settings of the tunnel itself are, maybe I don’t understand something.
Try to raise the tunnel first, and then encrypt it. Start with the simplest GRE:
blog.sedicomm.com/2017/11/11/kak-skonfigurirovat-g...