Oct 30, 2011

Abstract of CCNA study guide-1- internetworking 1

This is the beginning of our series for  Abstract CCNA study guide book .
First, you need to know exactly what an internetwork is, right?
You create an internetwork when you connect two or more LANs or WANs via a router and configure a logical network addressing scheme with a protocol such as IP.

Internetworking Basics
You can breaking up a really big network into a number of smaller ones Called network segmentation. You do this by using devices like routers , switches , and bridges

broadcast domain : the set of all devices on a network segment that hear all the broadcasts sent on that segment.

collision domains:(This is an Ethernet term used to describe a network scenario wherein one particular device sends a packet on a network segment, forcing every other device on that same segment to pay attention to it. At the same time, a different device tries to transmit, leading to a collision, after which both devices must retransmit, one at a time
HUBS hubs don’t segment a network; they just connect network segments together.
hub represents only one collision domain and only one broadcast domain.

- routers are used to connect networks together and route packets of data from one network to another. Routers, by default, break up a broadcast domain they provide a separate broadcast domain for each interface.
There are two advantage of using routers in network:
1- they don't forward broadcast by default
2- they filter network based on layer3information (Network layer )

Router functions
- packet switching
- packet filtering
- internetwork communication
- path selection

- switches aren’t used to create internetworks (they do not break up broadcast domains by default).
- The main purpose of a switch is to make a LAN work better by providing more bandwidth for the LAN’s users.

- Switches break up collision domains so each and every port on a switch represents its own collision domain.
- Switches create separate collision domains but a single broadcast domain.

- bridges and switches break up collision domains on a LAN .
- bridges only had 2 or 4 ports.
- You would use a bridge in a network to reduce collisions within broadcast domains and to increase the number of collision domains in your network so this provides more bandwidth for users.

Figure 1.1 shows how a network would look with all these internetwork devices in place.

Remember that the router will not only break up broadcast domains for every LAN interface,
it will break up collision domains as well.
Looking at the figure, how many collision domains and broadcast domains are in this internetwork? Hopefully, you answered nine collision domains and three broadcast domains!
Only routers break up broadcast domains by default. And since there are three connections, that gives you three broadcast domains.
The all-hub network is one collision domain; the bridge network equals three collision domains. Add in the switch network of five collision domains—one for each switch port—and you’ve got a total of nine.

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