CCNA

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

The Transport layer segments and reassembles data into a data stream.

UDP and TCP protocols work at this layer. UDP is a unreliable service. Reliable means that acknowledgments, sequencing and flow control will be used.

The Transport layer is responsible for providing mechanisms for multiplexing upper-layer applications, establishing sessioins and tearing down virtual circuits.

It hides details of any network-dependent information from the higher layers by providing transparent data transfer.

Can be connectionless or connection-oriented.

Flow Control

Ensures Data integrity.

Prevents a sending host on one side of the connection from overflowing the buffers on the receiving host.

The purpose is to provides the means for the receiver to govern the amount of data sent by the sender.

Connection-Oriented Communication

In reliable transport operation, a device that wants to transmit sets up a connection-oriented communication with a remote device by creating a session. This is the only concerned with the connection-oriented portion of the Transport layer

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.

It serves to organize the communication between systems in different modes: simplex, half duplex and full duplex

The Session Layer basically keeps different applications' data separate from other applications' data.

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