patrick.net

I'm not great at networking, but maybe that would be a network bridge? Maybe "remote network bridge" is a term for this?

The last para kinda sounds like what youre asking
https://community.openvpn.net/openvpn/wiki/293-what-is-the-principle-behind-openvpn-tunnels

Cable modem=> WAN side of the router1 and at LAN side => connect to all PCs and one port (long CAT5/6 cable) connected to router2 WAN side and on LAN side connect to all the PCs

Blue says

Cable modem=> WAN side of the router1 and at LAN side => connect to all PCs and one port (long CAT5/6 cable) connected to router2 WAN side and on LAN side connect to all the PCs

That would connect both sites to the internet, but not to each other. I am missing the part where the appliances bridge to each other.

Hircus says

The last para kinda sounds like what youre asking

Thanks, I will research this. I never heard of "tan" and "tap" before.

Check bridge, never tried it before
https://kb.netgear.com/24105/What-is-bridge-mode-and-how-do-I-set-it-up-on-my-Nighthawk-router?source=patrick.net
https://kb.netgear.com/20831/How-to-set-up-Bridge-mode-on-R6300-R6250-R6200?source=patrick.net
you might want to watch this video on how to set it up: https://re-rockspace-local.com/how-to-put-netgear-modem-in-bridge-mode/?source=patrick.net

HeadSet says

I am trying to join two sites on one Class C type network using the internet like a long LAN cable:

What's your use case?
"Type C" implies that it's something which you would be using for personal use or a small business, but then your problem statement sounds like a VPN between corporate network and field office. For the latter, check out "Site-to-Site VPN", but it may be too much for personal use.

Blue says

Check bridge, never tried it before

Thanks, but "Bridge" mode does not connect two sites over the internet. It just allows WiFi connection between two wired neworks at the same site.

mostly reader says

"Type C" implies that it's something which you would be using for personal use or a small business

Yes, Class C is suitable for 254 IP devices or less, like a small business or home. Since I am only going to have about 20 computers at one site and 10 or so at the other, Class C is plenty big.

HeadSet says

Yes, Class C is suitable for 254 IP devices or less, like a small business or home. Since I am only going to have about 20 computers at one site and 10 or so at the other, Class C is plenty big.

Does this - https://www.paloaltonetworks.com/cyberpedia/what-is-a-site-to-site-vpn?source=patrick.net - sound like what you want?

HeadSet says

Thanks, but "Bridge" mode does not connect two sites over the internet.

Sorry, I didn't read fully and misunderstood.
Like @mostly reader says, you need a tunnel between two sites.
To make 192.168.1.x network across the two sub nets, there got to be one DHCP server(comes within every router) active at one location. I will have to look at how to configure the net.

Blue says

To make 192.168.1.x network across the two sub nets, there got to be one DHCP server (comes within every router) active at one location. I will have to look at how to configure the net.

Just to be clear, DHCP or even manual addressing is the easy part. The hard part (for me, anyway) is how to use the Internet as essentially a long LAN cable to keep both sites in the same network. Long ago, routers used to come with VPN capability that allowed one to set up the same model on two sites and do a pint-to-point VPN. But today's router's VPNs are not point-to-point, but geared to allow one to hide the IP address while surfing porn. Some routers have a VPN receive capability, but require one to use software like OpenVPN to connect. That is more a secure remote access than a seamless network connection.