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Static Routing

Remote networks are added to the routing table either by configuring static routes or enabling a dynamic routing protocol. When the IOS learns about a remote network and the interface that it will use to reach that network, it adds that route to the routing table as long as the exit interface is enabled.

A static route includes the network address and subnet mask of the remote network, along with the IP address of the next-hop router or exit interface. Static routes are denoted with the code S in the routing table as shown in the figure. Static routes are examined in detail in the next chapter.

When to Use Static Routes

Static routes should be used in the following cases:
A network consists of only a few routers. Using a dynamic routing protocol in such a case does not present any substantial benefit. On the contrary, dynamic routing may add more administrative overhead.
A network is connected to the Internet only through a single ISP. There is no need to use a dynamic routing protocol across this link because the ISP represents the only exit point to the Internet.
A large network is configured in a hub-and-spoke topology. A hub-and-spoke topology consists of a central location (the hub) and multiple branch locations (spokes), with each spoke having only one connection to the hub. Using dynamic routing would be unnecessary because each branch has only one path to a given destination-through the central location.

Typically, most routing tables contain a combination of static routes and dynamic routes. But, as stated earlier, the routing table must first contain the directly connected networks used to access these remote networks before any static or dynamic routing can be used.

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