Layer 7 - The Application layer:
Data generated by and usable by software applications. The main protocol used at this layer is HTTP.
HTTP - Hyper Text Transfer Protocol
FTP - File Transfer Protocol
SMTP - SImple Mail Transfer Protocol
DNS - Domain Name Services
DHCP - Dynamic Host Configuration Protocol
IMAP - Internet Message Access Protocol
IRC - Internet Relay Caht
RDP - Remote Desktop Protocol
NFS - Network FIle System
NIS - Network Information SYstem
SMTP - Simple Mail Transfer Protocol
SNTP - Simple Network Time Protocol
SSH - Secure Shell / Remote Telnet
Layer 6 - The Presentation layer:
Data is translated into a form the application can accept. Some authorities consider HTTPS encryption and decryption to take place at this layer.
AFP - Apple Filing Protocol
ICA - Independent Computing Architecture (Citrix system core protocol)
LPP - Lightweidth Presentation Protocol
Layer 5 - The Session layer:
Controls connections between computers (this can also be handled at layer 4 by the TCP protocol).
NetBIOS - Network Basic Input/Output System
PAP - Password Authentication Protocol
PPTP - Point to Point Tunneling Protocol
RPC - Remote Procedure Call Protocol
Layer 4 - The Transport layer:
Provides the means for transmitting data between the two connected parties, as well as controlling the quality of service. The main protocols used here are TCP and UDP.
TCP - Transmission Control Protocol
UDP - User Datagram Protocol
MPTCP - Multipath TCP
Layer 3 - The Network layer:
Handles the routing and sending of data between different networks. The most important protocols at this layer are IP and ICMP.
Protocols that work on WANS
ICMP - Internet Control Message Protocol
IGMP - Internet Group Meanagement Protocol
IPsec - Internet Protocol Security
Layer 2.5 - (The ARP layer)
ARP allows an IPv4 to be encapsulated inside a frame.
Devices on a network maintain an ARP Cache (Table) which contains a list of IP to MAC address associations
ARP Cache age out entries about every 90 seconds to force ARP to continually re-resolve the Cache/Table data.
This is not to be confused with the MAC address table of a switch, which is separate.
The MAC address table maps the MAC to a port on a switch.
The ARP cache (table) maps the MAC to IP of connected devices.
Switches do not need an ARP table except when using SSH.
Packets are stored within frames when passed through a network.
Below is an example of the contents of an IP packet.
The Frame: | Destination MAC Address | Source MAC Address | Layer 3 Protocol |
The Packet inside the Frame: | Source IP Address | Destination IP Address | TTL | Other | ICMP |
Detail of Frame:
Destination MAC Address: Where the frame is being sent
Source MAC Address: Where the frame came from
Layer 3 Protocol: ARP, ICMP
The IP Packet:
Layer 2 - The Data link layer:
Handles communications between devices on the same network. If layer 3 is like the address on a piece of mail, then layer 2 is like indicating the office number or apartment number at that address. Ethernet is the protocol most used here.
Layer 2 = Protocols that work on LANS
PING - Packet Inter Networking Grouper
Ethernet - Broadcast / Flood / Multicast (LAN)
IEEE 802.11 Wireless LAN
IEEE 802.2 - provides LLC funstions to IEEE 802 MAC layers
Layer 1 - The Physical layer:
Packets are converted into electrical, radio, or optical pulses and transmitted as bits (the smallest possible units of information) over wires, radio waves, or cables.
Physical Ethernet - (10BASE5, 100BASE-TX, 100BASE-FX, 1000BASE-T, 1000BASE-SX)
802.11 WiFi-Physical Layer
ISDN - Integrated Services Digital Network
USB - Physical
Hardware - Router, Switch, Firewall