Internet Protocol Security (IPsec) is a protocol suite for securing Internet Protocol (IP) communications by authenticating and encrypting each IP packet of a communication session. IPsec also includes protocols for establishing mutual authentication between agents at the beginning of the session and negotiation of cryptographic keys to be used during the session.
IPsec is an end-to-end security scheme operating in the Internet Layer of the Internet Protocol Suite. It can be used in protecting data flows between a pair of hosts (host-to-host), between a pair of security gateways (network-to-network), or between a security gateway and a host (network-to-host)
What are IPSEC Policies?
An IPSec policy is nothing more than a set of rules that govern when and how Windows 2000 uses the IPSec protocol. The IPSec policy interacts directly with the IPSec driver. The policy tells Windows such things as which data to secure and which security method to use.
How to configure IPSEC encryption with the Cisco IOS (site to site VPN tunneling)
The OSPF dynamic routing protocol is probably the most popular LAN routing protocol today. OSPF can scale to the largest LANs but can also start out small. While OSPF can be complex to configure, its basic configuration isn’t difficult. Let’s learn how to configure OSPF in the Cisco IOS.
What do you need to know about OSPF?
IPSEC VPN Configuration in the Cisco IOS is not an easy task. For even experienced IT Pros, if you have never configured a Cisco IOS VPN, attempting to configure it can be frustrating and complex. In this article, we will look at a working Cisco IOS IPSEC VPN configuration and dissect the important parts to help you understand this very useful configuration.
By Petri again
And very interesting Illustrated Guide to IPsec by Steve Friedl