CCNA Cisco Certified Network Associate Study Guide - FTP Server

246 Chapter 5 � IP Routing
2501C(config-if)#no shut
2501C(config-if)#int s0
2501C(config-if)#ip address 172.16.40.2 255.255.255.0
2501C(config-if)#no shut
Interface Ethernet 0 is configured to participate in the 172.16.50.0 network,
and serial 0 is configured into the 172.16.40.0 WAN network. The
output of the show ip route command, displayed below, shows the directly
connected networks on router 2501C.
2501C#sh ip route
Codes: C - connected, S - static, I - IGRP, R - RIP,
M – [output cut]
Gateway of last resort is not set
172.16.0.0/24 is subnetted, 2 subnets
C 172.16.50.0 is directly connected, Ethernet0
C 172.16.40.0 is directly connected, Serial0
2501C#
Router 2501C can communicate with 2501B since they are on the same
WAN network. However, by default, 2501C cannot see any other router or
network.
IP Routing in Our Network
The network in the previous section has now been configured correctly
with IP addressing. However, how does a router send packets to remote networks?
The routers can only send packets by looking at the routing table and
discovering how to get to the remote networks. But our configured routers
only have information containing directly connected networks in each routing
table. What happens when a router receives a packet with a network that
is not listed in the routing table? It doesn’t send a broadcast looking for the
remote network—the router just discards it. Period.
There are a few different ways to configure the routing tables to include
all the networks in our little internetwork so that packets will be forwarded.
However, the best way for one network is not necessarily best for another.