Let's say a network admin is provided a /24 IP address and asked to create a network that involves two different subnetworks that are distant to each other. I have learned that I need to assign a subnetwork to the ppp connection. However, I need to be more economical about the number of subnetworks since we need to assign 40-50 host per each subnetwork. Is there a way to assign the rented ppp connection to be in the distant LAN so that I do not use a new subnetwork to assign to the connection of these two networks? PS: I also need to do that because I have a router firewall and as I know, these firewall needs to be assigned an IP from each subnetwork. If I start the new network from the other place, I can more easily give these IPs to the firewall.
Yes. IP unnumbered allows for this type of configuration on Cisco devices.
The ip unnumbered configuration command allows you to enable IP processing on a serial interface without assigning it an explicit IP address. The ip unnumbered interface can "borrow" the IP address of another interface already configured on the router, which conserves network and address space.