Layer 3 protocols – IP and ARP
The purpose of Layer 3 is to forward user information from end to end. This is usually from the user's PC, laptop, or smartphone to the organization's servers or to servers on the internet, but also in IoT devices and sensors, from cellphone to cellphone, and more.
In this section, we will examine the Internet Protocol version 4 (IPv4) and Address Resolution Protocol (ARP) that resolve the local destination MAC address from its IP address. We will discuss IPv4 next.
IPv4
As you can see in Figure 2.17, the layer-3 IP packet is carried inside the payload field of the layer-2 frame, usually Ethernet, and carries inside its payload the layer-4 protocol, which is usually UDP or TCP:
Important Note
An IP can be carried by layer-2 Ethernet or any other frame. Ethernet is the most common frame in layer 2, but an IP can be carried by cellular frames or any other layer 2.
Figure 2.17 – The IPv4 packet...
