Are subnet masks necessary?
Subnet masks are critical to communications on an IP network. Network devices use the IP address targets and defined netmask to determine if the network the host is on is a local subnet, or a remote network. This is important because devices act differently depending on the result. If the subnet is local, the device will send an ARP request to retrieve the MAC or hardware address of the system in question to communicate over the data-link layer. If the address is found to be on a remote network, then the network device routes packets to the gateway in it’s routing table that is set to handle that network. If no routing table entry is found matching that network, the packets are routed to the default route. If no default route is defined, the packets are dropped with nowhere left to go.
