Default Gateways
Default gateways are the means by which a device is able to access hosts on other networks for which it does not have a route. Most workstation configurations actually default to just using default gateways rather than having any static routes configured.
EXAM TIP
Default Gateways For the Network+ exam, you will be expected to identify the purpose and function of a default gateway.
When a system wants to communicate with another device, it first determines whether the host is on the local network or a remote network. If the host is on a remote network, the system looks in the routing table to determine whether it has an entry for the network that the remote host is on. If it does, it uses that route. If it does not, the data is sent to the default gateway.
NOTE
Default Gateway Must Be Local Although it might seem obvious, it's worth mentioning that the default gateway must be on the same network as the nodes that use it.
In essence, the default gateway is simply the path out of the network for a given device. Figure 6.11 shows an example of how a default gateway fits into a network infrastructure.
Figure 6.11. The role of a default gateway.
If a system is not configured with any static routes or a default gateway, it is limited to operating on its own network segment.