Decision Process with Local Subnet Destinations

Decision Process with Local Subnet Destinations

[View full size image]

Hosts do not always send packets to their default gateway. Instead, they start by asking a simple question: "Is the destination address of this packet in the same subnet that I am in?" If so, the host needs to send the packet directly, as shown in Figure 11-14. If the packet's destination is in a different subnet, the host simply needs to send the packet to its default router. So, each host computer knows the range of valid IP addresses in its own subnet, so all the computer has to do is compare the destination IP address of the packet to that list of valid addresses.

By the way, in either case, the host might need to use ARP to learn the MAC address either of the other host computer or the default gateway.