I've had to do this for a large Company / Enterprise about 20 years ago. They bought control of a company in Germany wanted their Networks hooked up.
Some luck. Despite using an unusual combination of 172.x.x.x as an enterprise network so was this company, both thinking it's unusual.
Long story cut short: I did it using a form of double Natting and a lookup table, mapping the entire Network of the subsidiary in Germany to another Network range. Today, it would be MUCH easier to do this.
You don't really want to!
* Having two networks with same IP ranges is always a BIG headache when troubleshooting.
* Is it my local server or remote server with the IP 192.168.1.23 causing problems?
* Or is my DNS showing the real server or the remote server?
* DNS is another BIG headache in double IP networks - no one really wants to go there!
* Monitoring two identical Networks with tools like Zabbix / Nagios / whatever is more work than benefit.
It is much easier, and definetely Best Practices if each node in the whole network (VPNs and all interconnected sites) have a consistant numbering / name scheme.
--> If possible, change the Network IP of one of the involved sites.
Also Best Advice for all of you in Networking:
NEVER set up a clients network using any of the following IP ranges:
A lot of Hardware like WLan Routers come preconfigured with IPs in that range. Now an employee buys himself a Wireless Router for Home use and thinks: Well, I have time in my break, I'll just hook it up to the LAN...
Now: if your main router also has that same IP, and worse, both are doing DHCP Services, it'll be within minutes that some host can do Internet and some can't. Or none - due to IP conflict!
Just evade those IP ranges, especially if you're free to set up the network!
My 2 cents!