Wer sagt denn das VPN´s bauen nicht witzig sein darf? Ein paar Erklärungen aus dem FreeBSD IPsec mini-HOWTO:

Some definitions you will need every day in business:

AH: This does not mean “aah nice”. It means authentication header.
= checksum for a packet, but no encryption
= if you have a shared secret you can be sure the packets are from the right sender.

ESP: This is not a shopping channel or a fuel station.
= Encryption / Decryption of packets by a shared secret

IKE: This has nothing to do with inverse kinematics.
= Mechanism to share secret keys between peers.

SPD: This is not a political group at this time.
= Database with rules where to get/send to data.

TIME: This is no configuration option, I just want to tell you that it takes time to understand this tutorial and IPSEC in general. If you have no time or if you are not willing to learn new things you will have a problem.

Besonders der letzte Punkt gefällt mir. So, und jetzt wieder an die Arbeit…