IP Routing is the
process use by a router to forward packets toward the destination network as
found in the routing table, which is created by routing algorithms or routing
protocols.
A router makes
decisions based upon the destination IP address of a packet. Routers don’t care
about hosts in a network, but networks and the best possible way to reach them.
All network devices along the way use the destination IP address to send the
packet in the right direction to reach its destination. To make the correct
decisions, routers must learn how to reach remote networks. Routers use either dynamic routing - this information is learned
from other routers, or static
routing - a network administrator configures information about remote networks
manually.
Although it’s deemed necessary
for every device in the network to be assigned a unique IP address, but this is
not sufficient for them to communicate. It’s the work of a router to acts as a
sort of traffic director to all packet destined to a destination.
In summary, routers route traffic
to all networks in your internetwork. For a router to be able to do this, it
must know the following:
i. Destination
address
ii.
Possible
routes to all networks
iii. Neighboring
routers from which it will learn about remote networks
iv. The
best route to reach a network
v.
How
to maintain and verify routing information.
Example below
shows how a router uses information in its routine table to make decisions:
R2#show IP route
[Output omitted]
Gateway of last
resort is not set
C 192.168.1.32/27 is directly
connected, fastEthernet0/1
C 192.168.1.0/27 is directly
connected, fastEthernet0/2
C 10.10.1.0/30 is directly
connected, serial 0/0/0
The C in the routing table means the networks are directly connected. The
remote networks are not found and displayed in the routine table because, we
have not added a routing protocol – such
as RIP, EIGRP, OSPF etc. etc or
configured Static routes.
Looking at the output above, when
the network router receive a packet with the destination address of
192.168.1.10, the router will send the packet to interface fastEthernet0/2, and
this interface will frame the packet and then send it out on the network
segment to Network B.
IP Routing Protocols
