Information Technology Reference
In-Depth Information
A
remote
network: This is a network that can only be reached by sending the packet to another
router. These networks are added to the routing table by using a
dynamic routing protocol
or by
configuring
static routes
.
Dynamic
routes are routes to remote networks that were learned auto-
matically by the router.
Static
routes are routes to networks that a network administrator manu-
ally configured.
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show ip route
Command
Describe the meaning of each part of the following route entry:
C 172.16.0.0/16 is directly connected, FastEthernet0/0
C:
The information in this column denotes the source of the route information, directly con-
nected network, static route, or a dynamic routing protocol. The C represents a directly con-
nected route.
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172.16.0.0/24:
This is the network address and subnet mask of the directly connected or remote
network.
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FastEthernet 0/0:
The information at the end of the route entry represents the exit interface
and/or the IP address of the next-hop router. In this example, both FastEthernet 0/0 and Serial
0/0/0 are the exit interfaces used to reach these networks.
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Static Routing
When the IOS learns about a remote network and the interface it will use to reach that network, it
adds that route to the
routing table
, as long as the
exit interface
is enabled.
Static routes are denoted with the code
S
in the routing table.
List and describe three situations in which static routes should be used.
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 can add more admin-
istrative overhead.
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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.
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A large network is configured in a hub-and-spoke topology.
A hub-and-spoke topology con-
sists of a central location (the hub) and multiple branch locations (spokes), with each spoke
having only one connection to the hub. Using a dynamic routing protocol would be unnecessary
because each branch only has one path to a given destination—through the central location.
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Dynamic Routing
Dynamic routing protocols are used by routers to share information about the reachability and status
of remote networks. Dynamic routing protocols perform several activities, including
Network discovery
, which is a routing protocol's ability to share information about the net-
works it knows about with other routers that are also using the same routing protocol
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Maintain
routing tables, which is a routing protocol's ability to compensate for any topology
changes without involving the network administrator
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