CCNA: Difference between revisions
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==OSI Layered Reference Model== | ==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)=== | ===Physical Layer (L1)=== | ||
Function: Physical topology | |||
* Movies bits between devices | * Movies bits between devices | ||
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===Data Link Layer (L2)=== | ===Data Link Layer (L2)=== | ||
Function: Framing | |||
* Combines packets into bytes and bytes into frames | * Combines packets into bytes and bytes into frames | ||
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===Network Layer (L3)=== | ===Network Layer (L3)=== | ||
Function: Routing | |||
* Provides logical addressing, which routers use for path determination | * Provides logical addressing, which routers use for path determination | ||
===Transport Layer (L4)=== | ===Transport Layer (L4)=== | ||
Function: End-to-end connection | |||
* Provides reliable or unreliable delivery | * Provides reliable or unreliable delivery | ||
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===Session Layer (L5)=== | ===Session Layer (L5)=== | ||
Function: Dialog control | |||
* Keeps different applications' data separate | * 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)=== | ===Presentation Layer (L6)=== | ||
Function: Data encryption, compression and translation services | |||
* Presents data | * Presents data | ||
* Handles processing such as encryption | * 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)=== | ===Application Layer (L7)=== | ||
Function: File, print, message, database and application services | |||
* Provides a user interface | * 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 | |||
Revision as of 18:51, 26 March 2010
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
They work at Layer 2
They break up "collision domains" only.
Routers (Layer 3 switches)
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
They break up collision domains.
Hubs
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 :
Error creating thumbnail: File missing
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:
Error creating thumbnail: File missing
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
