In the previous Internetworking episode (Part 2) we were primarily discussing the different topologies used within the context of computer networking. My teachers, instructors and professors all told me time and again to keep it simple. Well the difference between the topology used within a home, business, or the world is its scale. Obviously the scale on a global enterprise will be much larger and gander in nature. Just a few words of wisdom from one who has, time and again, made things out to be more difficult than they really were! Now, back to business…
A basic network can, in-fact, be just two computers. However, that would be it, but if you connect those two computers up to a hub there can be other computers connected up for a larger scale of communications. But as it was mentioned in a prior part, anything sent to the hub will be broadcasted to all other nodes connected to that hub. That is why a switch is preferred as it is a smart hub and can learn who is connected to it and direct data out specific ports. Another problem with a hub is that you are forced to share your bandwidth with all other hosts that are connected to it, which can really cramp your style as far as sending out data from all devices at any given time.
You can take a very large network and segment it in to much smaller more efficient and functional networks by using devices such as routers, switches, or bridges. Each device connected to the switch is on a separate collision domain; however, the switch itself is all one broadcast domain. With the figure (<- to the left) you can see that there is one broadcast domain with three separate collision domains. Notice that one of the collision domains was extended with a hub, which must share the bandwidth between two host devices. There are times you may wish to do this, sometimes cost effectiveness outweighs network efficiency.
Just a note: Keep in mind that routers are in-fact switches; however, switches work at Layer 2 (the Data Link Layer) where routers work at Layer 3 (the Network Layer) – we will discuss the Layers at a later time.
Routers are used to connect networks together, create an internetwork, and provide connections to wide area networks (WANs). As mentioned, the router breaks up broadcast domains. As you can see (to the right ->) a router is connected to two separate switches creating two separate broadcast domains. The two switches are connected to two separate hosts, which created four separate collision domains.
Here are some common local area network (LAN) congestion:
- Too many hosts in a broadcast domain
- Broadcast storms
- Low bandwidth
- Adding hubs for connectivity
The two advantages of using routers in a network are:
- They don’t forward broadcasts by default
- They can filter the network traffic based upon layer 3 (Network layer) information (the IP addressing)
There are four functions the router performs:
- Packet switching
- Packet filtering
- Internetwork communication
- Path selection
The difference between a switch and a bridge is that the switch has more ports and more brain power. Switches, bridges, and hubs are used to extend certain functionality to the network. Each has a purpose, however, as technology grows and expands – older technology seems to fade away into the history books. There are many instructors who like the hubs for teaching and testing purposes, but are unable to find them. When they do find some and purchase them, they are not the Real McCoy. Hubs are especially useful for penetration testing by use of white hat hacking.
Until the next exciting adventure!
CCNA Cisco Certified Network Associate Study Guide, 6th Ed, Todd Lammle