Ccna routing and Switching Complete Study Guide

IPsec Transforms

An IPsec transform specifies a single security protocol with its corresponding security 

algorithm; without these transforms, IPsec wouldn’t be able to give us its glory. It’s 

important to be familiar with these technologies, so let me take a second to define the 

security protocols and briefly introduce the supporting encryption and hashing algorithms 

that IPsec relies upon.

Security Protocols

The two primary security protocols used by IPsec are Authentication Header (AH) and 

Encapsulating Security Payload (ESP).

Authentication Header (AH)

The AH protocol provides authentication for the data and the IP header of a packet using a 

one-way hash for packet authentication. It works like this: The sender generates a one-way 

hash; then the receiver generates the same one-way hash. If the packet has changed in any 

way, it won’t be authenticated and will be dropped since the hash values won’t match. So 

basically, IPsec relies upon AH to guarantee authenticity. AH checks the entire packet, but 

it doesn’t offer any encryption services.

This is unlike ESP, which only provides an integrity check on the data of a packet.