- IP routing is basically the process
of moving packets from one network to another
using routers.
It's essential to networking because
it pertains to all routers
and configurations that use it.
And by routers, I mean Cisco routers, of course.
The term router and layer 3 device
are practically interchangeable.
So, throughout this video when I use the term router,
I'm referring to any layer 3 device.
Before jumping into this further,
I want to explain the difference between
a routing protocol,
and a routed protocol.
Routers use routing protocols to
dynamically find all networks within
the greater internetwork,
and to ensure that all routers have the same
routing table
which is a map of the internetwork.
Routing protocols are also employed
to determine the best path a packet
should take through an internetwork
to get to its destination most efficiently.
RIPv2, EIGRP, and OSPF are great examples
of the most common routing protocols.
Once all routers know about all networks,
a routed protocol can then be used to send
user data, i.e. packets,
through the established enterprise.
Router protocols are assigned to an interface,
and determine the method of packet delivery.
Examples of common router protocols are IP and IPv6.
Once you create an internetwork by connecting
your WANs and LANs to a router,
you'll need to configure a logical
network address like IP
to all hosts on the internetwork
for them to communicate successfully throughout it.
The term routing refers to taking a packet
from one device,
and sending it through the network
to another device on a different network.
Routers really don't care about hosts
they only care about networks,
and the best path to each one of them.
The logical network address of the destination host
is key to get packets through a routed network.
It's the hardware address of the host
that's used to deliver the packet from a router,
and ensure it arrives at the correct destination host.
Routing is irrelevant if your network
has no routers
because their job is to route traffic
to all networks in your internetwork.
But this is rarely the case.
There are five minimum factors
a router must know to effectively route packets.
The destination address,
neighbor routers from which it can learn
about remote networks,
possible routes to all remote networks,
the best route to each remote network,
and to maintain and verify routing information.
The router learns about remote networks
from neighboring routers,
or from an administrator.
The router, then, builds a routing table
which is basically a map of the internetwork,
and it describes how to find remote networks.
If a network is directly connected,
then the router already knows how to get to it.
That's the default.
But if a network isn't directly connected to the router,
the router must use one of two ways
to learn how to get to a remote network.
Static routing,
which requires someone to hand type
all network locations, and changes,
into the routing table.
Which can be a pretty daunting task
when used on all but the smallest of networks.
Conversely, when dynamic routing is used
a protocol on one router
communicates with the same protocol
running on neighboring routers.
The routers then update each other
about all the networks they know about,
and place this information into the routing table.
If a change occurs in the network,
the dynamic routing protocols automatically
inform all routers about the event.
If static routing is used,
the administrator is responsible
for updating all changes by hand
into all routers.
Most people usually use a combination
of dynamic and static routing
to administer a large network.
So, just remember
IP routing is the process of moving
packets from one network to another,
and we do this by using Cisco routers.