Categories
CCNP Enterprise Core (350-401) Cisco Packet Forwarding

Network Device Communication

The primary function of the network is to provide connectivity between devices. In the past there was a huge variety of different network protocols but today almost everything is based on Traffic Control Protocol/Internet Protocol (TCP/IP).

TCP/IP is based upon the Open Systems Interconnection (OSI) model that is made up of seven layers. Each layer of the OSI model is a specific function of network communcation between two devices.

LayerNameDescription
7ApplicationInterface for receiving and sending data
6PresentationFormatting of the data and encryption
5SessionTracking of packets across a connection
4TransportEnd to end communcation between the devices
3NetworkLogical addressing and the routing of packets
2Data LinkHardware addressing of devices
1PhysicalMedia type such as wiring, and connector
The OSI Model

Applications generate data at Layer 7 of the OSI model, and the device sends this data down each layer of the OSI model. Once the data begins to reach Layer 3, the nework layer, the host needs to determine whether this datra needs to be sent to an application on the same device or to continue working its way down the layers until it reaches Layer 1.

Layer 1 is responsible for getting the data values from one device other to the destination device. Once it reaches the destination device the data works its way back up the layers to deliver the network data to the application.

At Layers 2 and 3 network devices can forward traffic on a Layer 2 or 3 perspective from one device to another. In the beginning the first Layer 2 devices were bridges or switches, and Layer 3 devices were routers.

Technology advancements allowed the use of Application Specific Integrated Circuit (ASIC) chips to route and switch packets faster in hardware. As these technologies continued to advanced, multilayer switches came along to switch traffic at Layer 2 as if they were switches but also route traffic at Layer 3 as if they were routers.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.