Elements of IP Routing 4-5
Routing Table With a routing table, a router or host determines how to send a packet
toward its ultimate destination. The routing table contains an entry for
every network, subnetwork, and host to which the router or host can
forward packets. A router or host uses the routing table when the
packet’s destination IP address is not on a network or subnetwork to
which it is directly connected. The routing table provides the IP address of
a router that can forward the packet toward its destination.
The routing table consists of the following elements:
■ Destination IP address — The destination network, subnetwork, or
host.
■ Subnet mask — The subnet mask for the destination IP address.
■ Metric — A measure of the distance to the destination. In the
Routing Information Protocol (RIP), the metric is the number of hops
through routers.
■ Gateway — The IP address of the router interface through which the
packet travels on its next hop.
■ Status — Information that the routing protocol has about the
interface.
Figure 4-5 shows the routing table of the router in Figure 4-4.
Figure 4-5 Sample CoreBuilder 2500 Routing Table
Routing table
158.101.1.1
158.101.2.1
158.101.3.1
default route
Destination IP address
Status
learned - RIP
learned - OSPF - INTRA
learned - OSPF - INTRA
learned - OSPF - INTRA
Gateway
158.101.1.2
158.101.2.2
158.101.3.2
158.101.1.2
Metric
1
1
1
1
Subnet mask
255.255.255.0
255.255.255.0
255.255.255.0
255.255.255.0
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