HTTP is the application protocol that powers the Web. It began life as the so-called HTTP/0.9 protocol in 1991, and by 1999 had evolved to HTTP/1.1, which was standardised within the IETF (Internet Engineering Task Force). HTTP/1.1 was good enough for a long time but the ever changing needs of the Web called for a better suited protocol, and HTTP/2 emerged in 2015. More recently it was announced that the IETF is intending to deliver a new version - HTTP/3. To some people this is a surprise and has caused a bit of confusion. If you don’t track IETF work closely it might seem that HTTP/3 has come out of the blue. However, we can trace its origins through a lineage of experiments and evolution of Web protocols; specifically the QUIC transport protocol.

IPSec modes are closely related to the function of the two core protocols, the Authentication Header (AH) and Encapsulating Security Payload (ESP). Both of these protocols provide protection by adding to a datagram a header (and possibly other fields) containing security information. The choice of mode does not affect the method by which each generates its header, but rather, changes what specific parts of the IP datagram are protected and how the headers are arranged to accomplish this. In essence, the mode really describes, not prescribes how AH or ESP do their thing. It is used as the basis for defining other constructs, such as security associations (SAs).

Let’s take a look at how the two modes work.

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