Unixwiz.net: An Illustrated Guide to IPSec

“IPSec is a suite of protocols for securing network connections,
but the details and many variations quickly become overwhelming.
This is particularly the case when trying to interoperate between
disparate systems, causing more than one engineer to just
mindlessly turn the knobs when attempting to bring up a new

“This Tech Tip means to give bottom-up coverage of the low-level
protocols used in an IPv4 context (we provide no coverage of IPv6).
This is not a deployment guide or best-practices document–we’re
looking at it strictly at the protocol level on up, rather than
from the big picture on down…”