What does the OSI model stand for and what are the seven layers?
Open Systems Interconnection Reference Model
Layer 7 = Application
Layer 6 = Presentation
Layer 5 = Session
Layer 4 = Transport
Layer 3 = Network
Layer 2 = Data Link
Layer 1 = Physical
Describe layer 1 of the OSI model
Physical layer -- signaling, cabling, connections
No protocols
Examples of layer 1 issues and solutions
Fix cabling, punch-downs, etc.
Run loopback tests, test/replace cables, swap adapter cards
Loopback test
A diagnostic procedure that verifies the integrity of a communication pathway by sending a signal
from a device and returning it to the same device
,Describe layer 2 of the OSI model
Data Link layer, the basic network "language", the foundation of communication
* MAC address on Ethernet
The "switching" layer
Describe layer 3 of the OSI model
Network layer, the "routing layer"
* Internet Protocol (IP)
* Fragments frames to traverse different networks
Describe layer 4 of the OSI model
Transport layer, the "post office" layer, parcels and lettings from one side of the network to the other
* TCP & UDP
Describe layer 5 of the OSI model
Session layer, communication between devices (start, stop, restart)
* Control protocols, tunneling protocols
Describe layer 6 of the OSI model
Presentation layer
* Character encoding
* Application encryption
* Often combined with layer 7, the application layer
,Describe layer 7 of the OSI model
Application layer, the layer we see
* HTTP, FTP, DNS, POP3
OSI model mapped to real-world
Layer 7 = Your eyes
Layer 6 = Application encryption (SSL/TLS)
Layer 5 = Control protocols, tunneling protocols
Layer 4 = TCP segment, UDP datagram
Layer 3 = IP Address, Router, Packet
Layer 2 = Frame, MAC address, Extended Unique Identifier (EUI-48, EUI-64), Switch
Layer 1 = Cables, fiber, and the signal itself
Real-world example of the OSI model
Application: https://mail.google.com
Presentation: SSL encryption
Session: Link the presentation to the transport
Transport: TCP encapsulation
Network: IP encapsulation
Data Link: Ethernet
Physical: Electrical signals
, Router
- Routes traffic between IP subnets
- OSI layer 3 devices
- Routers inside of switches sometimes called "layer 3 switches"
- Often connects diverse network types
* LAN, WAN, copper, fiber
Switch
- Forwards traffic based on data link address
- May provide PoE (Power over Ethernet)
Multilayer switch
includes layer 3 (routing) functionality
Application-specific integrated circuit (ASIC)
Type of processor designed to perform a specific function, such as switching.
Firewall
- Filters traffic by port number or application
- Encrypts traffic, VPN between sites
- Most firewalls can be layer 3 devices (routers)
* Network Address Translation (NAT)
* Dynamic routing
Open Systems Interconnection Reference Model
Layer 7 = Application
Layer 6 = Presentation
Layer 5 = Session
Layer 4 = Transport
Layer 3 = Network
Layer 2 = Data Link
Layer 1 = Physical
Describe layer 1 of the OSI model
Physical layer -- signaling, cabling, connections
No protocols
Examples of layer 1 issues and solutions
Fix cabling, punch-downs, etc.
Run loopback tests, test/replace cables, swap adapter cards
Loopback test
A diagnostic procedure that verifies the integrity of a communication pathway by sending a signal
from a device and returning it to the same device
,Describe layer 2 of the OSI model
Data Link layer, the basic network "language", the foundation of communication
* MAC address on Ethernet
The "switching" layer
Describe layer 3 of the OSI model
Network layer, the "routing layer"
* Internet Protocol (IP)
* Fragments frames to traverse different networks
Describe layer 4 of the OSI model
Transport layer, the "post office" layer, parcels and lettings from one side of the network to the other
* TCP & UDP
Describe layer 5 of the OSI model
Session layer, communication between devices (start, stop, restart)
* Control protocols, tunneling protocols
Describe layer 6 of the OSI model
Presentation layer
* Character encoding
* Application encryption
* Often combined with layer 7, the application layer
,Describe layer 7 of the OSI model
Application layer, the layer we see
* HTTP, FTP, DNS, POP3
OSI model mapped to real-world
Layer 7 = Your eyes
Layer 6 = Application encryption (SSL/TLS)
Layer 5 = Control protocols, tunneling protocols
Layer 4 = TCP segment, UDP datagram
Layer 3 = IP Address, Router, Packet
Layer 2 = Frame, MAC address, Extended Unique Identifier (EUI-48, EUI-64), Switch
Layer 1 = Cables, fiber, and the signal itself
Real-world example of the OSI model
Application: https://mail.google.com
Presentation: SSL encryption
Session: Link the presentation to the transport
Transport: TCP encapsulation
Network: IP encapsulation
Data Link: Ethernet
Physical: Electrical signals
, Router
- Routes traffic between IP subnets
- OSI layer 3 devices
- Routers inside of switches sometimes called "layer 3 switches"
- Often connects diverse network types
* LAN, WAN, copper, fiber
Switch
- Forwards traffic based on data link address
- May provide PoE (Power over Ethernet)
Multilayer switch
includes layer 3 (routing) functionality
Application-specific integrated circuit (ASIC)
Type of processor designed to perform a specific function, such as switching.
Firewall
- Filters traffic by port number or application
- Encrypts traffic, VPN between sites
- Most firewalls can be layer 3 devices (routers)
* Network Address Translation (NAT)
* Dynamic routing
