Layer 4 - Transport Layer

Summary

Layer 4 is known as the host-to-host or the end-to-end layer. The Transport Layer helps identify the ports that need to be used to communicate in each application in data attached to the packet called segments.

How it works

The transport layer appends a port number to the source and destination network addresses in the form of segments. Other layers will ignore this portion and see it as just part of the payload.

Redlivery

Redlivery can be requested from source hosts when a package is corrupted and does not have the correct information or may not have received a package it expected.

Firewalls

Firewalls can be implemented at this layer where packets may only be sent or received from certain sources on port(s).

Devices

• Switches
• Load Balancers
• Security Appliances like Advanced Firewalls and Intrusion Detection Systems (IDS).