In a common configuration, routers are used to create larger
networks by joining two network segments. Such as a SOHO router used to connect
a user to the Internet. A router can be a dedicated hardware device or a
computer system with more than one network interface and the appropriate
routing software. All modern network operating systems include the
functionality to act as a router.
A router derives its name from the fact that it can route data it
receives from one network onto another. When a router receives a packet of
data, it reads the header of the packet to determine the destination address.
Once it has determined the address, it looks in its routing table to determine
whether it knows how to reach the destination and, if it does, it forwards the
packet to the next hop on the route. The next hop might be the final
destination, or it might be another router. Figure 5 shows, in basic terms, how
a router works.
A router derives its name from the fact that it can route data it
receives from one network onto another. When a router receives a packet of
data, it reads the header of the packet to determine the destination address.
Once it has determined the address, it looks in its routing table to determine
whether it knows how to reach the destination and, if it does, it forwards the
packet to the next hop on the route. The next hop might be the final
destination, or it might be another router.
How a router works?
As you can see from this example, routing tables play a very important
role in the routing process. They are the means by which the router makes its
decisions. For this reason, a routing table needs to be two things. It must be
up-to-date, and it must be complete. There are two ways that the router can get
the information for the routing table through static routing or dynamic
routing.
Static Routing
In environments that use static routing, routes and route
information are entered into the routing tables manually. Not only can this be
a time-consuming task, but also errors are more common. Additionally, when
there is a change in the layout, or topology, of the network, statically
configured routers must be manually updated with the changes. Again, this is a
time-consuming and potentially error-laden task. For these reasons, static
routing is suited to only the smallest environments with perhaps just one or
two routers. A far more practical solution, particularly in larger
environments, is to use dynamic routing.
Dynamic Routing
In a dynamic routing environment, routers use special routing
protocols to communicate. The purpose of these protocols is simple; they enable
routers to pass on information about themselves to other routers so that other
routers can build routing tables. There are two types of routing protocols usedthe
older distance vector protocols and the newer link state protocols.
Dynamic Routing
In a dynamic routing environment, routers use special routing
protocols to communicate. The purpose of these protocols is simple; they enable
routers to pass on information about themselves to other routers so that other
routers can build routing tables. There are two types of routing protocols
usedthe older distance vector protocols and the newer link state protocols
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