The picture above is all 7 layers of the OSI Model. How do we use this? Well let’s say there’s an outage. You try to ping the device and do not get results. Well, we do not have to worry about layers 4 and above. This model can also help you decide what cables you need. Straight through cables need to be connected when dealing with different devices on the OSI model. You will need a cross over cable to connect devices on the same OSI layer.
I will try to simplify even more.
Layer 1 – Physical layer (Think cables and/or hubs) uses bits to communicate.
Layer 2 – Data link (switches) uses frames to communicate.
Layer 3 – Network (Routers, hosts, firewalls) – uses packets to communicate.
Layer 4- Transport (UDP, TCP) – Technically a firewall works at layer 4 but it’s mostly going to be TCP or UDP.