Cases may occur when a local network includes say around 300 computers. In these instances, one C class network is not enough and therefore two C class networks are assigned. Using two separate C class networks creates the danger of incorrect configuration. The LAN must have a router for routing between them (or a proxy ARP must be used). Instead of communicating within the network directly with each other, the computers must use the router. But the real drawback is that the data is transferred twice, once from the sender to the router and for a second time from the router to the recipient, which is most cumbersome with 300 computers in the network.
A reasonable solution is to use a super-network consisting of two C class networks, i.e., a super‑network with the mask /23, i.e., 255.255.128.0.
Figure 6.9: The most common firewall connections