CCENT And Network+ 2012 Tutorial

Introduction To The Routing Process

By Chris Bryant, CCIE #12933

Routing can and does get complicated at times, in both production networks and your advanced networking studies.

However, you'll make things a lot easier on yourself and your network when you master the fundamentals of networking - not to mention passing your CCENT and Network+ exams!

Let's take a look at the basic routing process - and that process really starts with the router asking itself one question:

"Do I know how to get this packet from Point A to Point B?"

Routers run at Layer 3 of the OSI model, handle packets, and examine their routing tables to see where to packets.

Routers can be configured with static routes, but most likely they'll be using one of the following protocols to dynamically exchange routes with other routers.

Routing Information Protocol (RIP)

Open Shortest Path First (OSPF)

Enhanced Interior Gateway Routing Protocol (EIGRP)

You'll master the fundamentals of these protocols during your CCNA studies (and by using the tutorials and videos on my CCNA Tutorials page), but the basics of routing remain the same.

In the following network, the PC on the 10.0.0.0 /8 network wants to send a packet to the PC on the 20.0.0.0 /8 network.

If the sending PC is configured to use the router as its default gateway, the PC will send the packet to the router. Hopefully for those packets, the router knows how to get the packets to the 20.0.0.0 /8 network.  (Devices that connect different or dissimilar networks are called gateways.)

The router knows where 20.0.0.0 /8 is because it's directly connected to that network -- no static route or dynamically discovered route is necessary.

Think of a router's directly connected route as a street that your car is parked on. You don't need directions to that street - you're already on it!

When the router sees an incoming packet with a destination IP address of 20.1.1.2, the router will check its routing table, see that it's directly connected to that network on its interface Ethernet1, and forward the packet.

Routing protocols become necessary when packets need to be routed to networks the router is not directly connected to, and that's the case more often than not, as in the following network.

In this network, the first router is receiving a packet destined for 30.1.1.2.  The router is not directly connected to the 30.0.0.0 /8 network, so that router must receive a dynamic routing update from another router telling it how to get packets to the 30.1.1.0 /8 network.  Without that dynamic route, the router will simply drop the packet.

These two examples are about as simple as routing gets!

For over 400 additional videos, tutorials, and practice exams to ensure you master the skills needed to earn your CCENT, CCNA, and Netowrk+ certifications, visit my Tutorials page - and these additional pages!

CCNA 3-Minute Video Boot Camps

My YouTube CCNA And CCNP Video Channel

CCNA Practice Exams

My CCNA On-Demand Video Boot Camp brings you over 20 hours of my clear, comprehensive CCNA training --

-- and I guarantee you can watch the videos as often as you like until you pass!

To your success,

Chris Bryant

CCIE #12933

chris@thebryantadvantage.com