1-2
s the routes found by all protocols and determines the optimal routes that
acket forwarding. The selection of an optimal route
ols and metrics of routes.
C
e
A ro
z
z
nd
z
z
of the next hop.
n but having different nexthops may have
outing protocols or manually configured. The optimal
(with the smallest metric).
rded through the default route.
In
Figure 1-1
z
A local routing table store
the router will deliver to the FIB table to guide p
is based on the preferences of routing protoc
ont nts of a routing table
uting table includes the following key items:
Destination address: Destination IP address or destination network.
Network mask: Specifies, in company with the destination address, the address of the destination
network. A logical AND operation between the destination address and the network mask yields
the address of the destination network. For example, if the destination address is 129.102.8.10 a
the mask 255.255.0.0, the address of the destination network is 129.102.0.0. A network mask is
made of a certain number of consecutive 1s. It can be expressed in dotted decimal format or by the
number of the 1s.
Outbound interface: Specifies the interface through which the IP packets are to be forwarded.
IP address of the next hop: Specifies the address of the next router on the path. If only the
outbound interface is configured, its address will be the IP address
z
Priority for the route. Routes to the same destinatio
different priorities and be found by various r
route is the one with the highest priority
Routes can be divided into two categories by destination:
z
Subnet routes: The destination is a subnet.
z
Host routes: The destination is a host.
Based on whether the destination is directly connected to a given router, routes can be divided into:
z
Direct routes: The destination is directly connected to the router.
z
Indirect routes: The destination is not directly connected to the router.
To prevent the routing table from getting too large, you can configure a default route. All packets without
matching any entry in the routing table will be forwa
, the IP address on each cloud represents the address of the network. Router G is
connected to three networks and therefore has three IP addresses for its three physical interfaces. Its
routing table is shown under the network topology.
