CCNA

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WHAT

I'm trying to study to get my CCNA (640-802) degree :D I'm using my wiki to note what I'm trying to learn ! Much of the stuff here are from SYBEX CCNA Study guide (6th edition). Hope it'll help other people.

Software

I'm using GNS3 to emulate a Cisco environment. Get it from GNS3 Homepage

Internetworking Devices

Switches

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They work at Layer 2

They break up "collision domains" only.

Routers (Layer 3 switches)

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They work at Layer 3

Cisco calls them multiport bridges.

Advantages:

  • They break up "broadcast domains" by default ( 1 broadcast domain per interface ).
  • They break up "collision domains".
  • Can filter network based on Layer 3 ( Network Layer ) information ( e.g., IP Address )

Useful at:

  • Packet switching
  • Packet filtering
  • Internetwork communication
  • Path selection

Bridges

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They break up collision domains.



Hubs

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They keep all hosts in the same collision domain.

They often cause traffic congestion if on a busy network.

Traffic Congestion

Can be caused by:

  • Too many hosts in a broadcast domain
  • Broadcast storms
  • Multicasting

TEST

Test 1

Do you _SEE_ the "collision domains" and "broadcast domains" here :

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9 collision domains

- All hub network - 1 collision domain

- The bridge network - 3 collision domains

- The switch network - 5 collision domains

3 broadcast domains

- Only the router breaks up broadcast domains ! It has 3 connections.

Test 2

Do you _SEE_ the "collision domains" here:

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10 "collision domains"

OSI Layered Reference Model

L1-L4 Define how data is transmitted end to end L5-L7 Define how applications within the end stations will communicate with each other and with users.

Physical Layer (L1)

Function: Physical topology

  • Movies bits between devices
  • Specifies voltage, wire speed and pin-out of cables

Data Link Layer (L2)

Function: Framing

  • Combines packets into bytes and bytes into frames
  • Provides access to media using MAC address
  • Performs error detection not correction

Network Layer (L3)

Function: Routing

  • Provides logical addressing, which routers use for path determination

Transport Layer (L4)

Function: End-to-end connection

  • Provides reliable or unreliable delivery
  • Performs error correction before retransmit

Session Layer (L5)

Function: Dialog control

  • Keeps different applications' data separate

The Session Layer is responsible for setting up, managing and then tearing down sessions between Presentation layer entities.

Presentation Layer (L6)

Function: Data encryption, compression and translation services

  • Presents data
  • Handles processing such as encryption

The Presentation layer presents data to the Application layer and is responsible for data translation and code formating.

Application Layer (L7)

Function: File, print, message, database and application services

  • Provides a user interface

Applications residing in the Application Layer: FTP, TFTP

The Application layer is acting as an interface between the actual application programs