What's the protocol-level difference between IPSec and "Cisco IPSec"?

Most VPN clients distinguish between IPSec and "Cisco IPSec." For example, (Apple's) iOS treats them as essentially separate things.

But I can't find any explanation of what the protocol-level differences are. They may be minor, but there definitely appear to be differences.

Can someone shed light on this? Even just a pointer to a detailed explanation would help a great deal. Thanks!

Solution 1:

From my understanding, "Cisco IPSec" is just marketing speak for IPSec with some pre-defined settings for AH/ESP, tunnel/transport mode, etc. pp.

When you read the RFCs, you see that they deliberately leave room for implementations...you, as the network admin setting up the IPSec connection have quite a lot of options to choose from for the protocol (and you need to). Cisco simplified this a great deal by saying "Both participiants do ESP, they have encryption modes X, Y, Z at their disposal, (...)".