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

Physical Layer (L1)

• Movies bits between devices

• Specifies voltage, wire speed and pin-out of cables

Data Link Layer (L2)

• Combines packets into bytes and bytes into frames

• Provides access to media using MAC address

• Performs error detection not correction

Network Layer (L3)

• Provides logical addressing, which routers use for path determination

Transport Layer (L4)

• Provides reliable or unreliable delivery

• Performs error correction before retransmit

Session Layer (L5)

• Keeps different applications' data separate

Presentation Layer (L6)

• Presents data

• Handles processing such as encryption

Application Layer (L7)

• Provides a user interface