Difference between each layer

- Layer 2 Data link layer (Ethernet)

Unit : Frame

Header : Includes MAC address of source and destination

Source broad casts the data and can receive data who has destination MAC address.

- Layer 3 Network Layer (IP)

Unit : Packet

Header : Includes IP addresses of source and destination

Use routing to distinct the network.

Routing table has IP and route information to find best route.

- Layer 4

Transport Layer (TCP/UDP)

Header : Use port to networking. http, ftp, smtp etc

Load balancing on the server farm environment

- Layer 7

Application Layer

To overcome L4's limitation.

Using more informations to networking : Data payloads (IP, port, URL, cookies, FTP file name, SSL ID, virus pattern etc)