Routers are a very important networking devices and without them the Internet wouldn’t exist. One good thing about getting your Cisco Certification is that a majority of the routers that run the Internet are made by Cisco. In other words there is going to be a demand for Cisco Certified Network Associates for a long time. I would even say that routers are more important to study about than switches for the ICND1 Exam because knowing how a router works requires knowledge about IP Addresses, subnetting, and routing protocols which are all important topics on the ICND1 Exam.
Routers are in charge of path selection
When I think about routers I like to visualize large freeway intersections with overpasses, loops, and many forks in the road. Well, that large complex intersection is the router and one of its important jobs is path selection.
Path Selection is important because many times there is more than one path to a destination. For example today I needed to go to the bank and I got in the right lane so that I could turn right on to Eagle Road (A large busy road here in Boise, ID) and a realized that there was an accident and that traffic was backed up. I quickly decided to change my path and take a longer route, but on a road that is far less congested. Because I made that choice I’m sure I got to the bank a lot quicker than everybody else stuck on Eagle Road.
Routing Tables are used to make a map of the network
Just like how I had the bank in mind as a destination each packet that your computer sends out has a destination IP Address attached to it. When these packets arrive at the nearest router, the router will look at the destination IP Address and compare it to its routing table to determine the best possible route. Each router has its own routing table and its kinda like a personal map they all have of the network. Routing tables show which interfaces to forward packets out of so that they can get to their destination.
Routing Protocols are used to communicate updates
In order for routers to know what the best possible route is, they need to have good communication by sending out regular updates to each other. If a path gets congested the router connected to this path will tell its neighbors about it so that they can determine if a different route should be taken. Routers protocols like RIPv2, OSPF, and EIGRP allow this communication to take place. Routing protocols determine how often updates get sent to each other and also have different preferences about path selection. For the ICND1 Exam you will need to know all about RIPv2.
Routers allow for networks to grow and to be fast
I know I’ve been talking a lot about path selection, but probably the most important thing about routers is that they allow networks to become really large and still maintain a healthy fast network!
A group of computers and switches are called broadcast domains. Routers do not forward broadcasts and so they allow networks to grow by breaking up these broadcasts domains into smaller manageable sizes. A broadcast is an IP Packet that is addressed to every single computer inside the broadcast domain and if there are a lot of broadcasts being sent out they can really slow down a network. By breaking up networks with routers that don’t send broadcasts the network is able to grow and not become congested.
I plan on going into more detail on all of these subjects so stay tuned and keep studying hard for your ICND1 Exam!
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