The TCP/IP Reference Model and Layers

The TCP/IP model is a more concise take on the OSI model.

• The TCP/IP model contains four layers:
  1. Process/Application Layer
  2. Host-to-Host/Transport Layer
  3. Internet Layer
  4. Network Access Layer/Link Layer

Network Access Layer

The Network Access Layer defines how to use the network to transmit an IP datagram, or unit of information packet.

• The Network Access Layer is:
  • the lowest layer
  • physical, data link, network
  • a directly attached network
  • the protocols provide the means for the system to deliver data to other directly (physically) attached network devices.
  • must be able to know the details of the underlying network (packet structure, addressing, etc.)

Gateways are devices that switch packets between different physical networks.

Routing is deciding which gateway to use.

Routers—all routers examine packets and then send them to the proper destination.

Internet Layer

Routing Table—tells the router exactly where to send the packets.

The Routing Table is KEY to understanding and controlling the process of sending packets to their proper destination.

Default Gateway—the router interface that connects a single LAN to the router. (The default gateway is the router for the subnetwork that you are on at the moment. The on-ramp to the greater, wider internet!)

Routers use network IDs to determine traffic.