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Dave Peck
Asked: 2011-11-23 14:11:38 +0800 CST

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

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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!

vpn cisco ipsec network-protocols protocol

2 Answers

  1. Best Answer

    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, (...)".

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  2. I understand from your comment that you are wondering the differences between L2TP+IPSec and IPSec only.

    • L2TP is a tunneling protocol. No encryption.
    • IPSec is a security protocol (encryption + authentication)

    When IPSec is used "alone", it can oper in two modes :

    • "tunnel": The tunnel is in fact a GRE tunnel (IP in IP), but the payload is encrypted.
    • "transport": IP payload is encrypted, without any encapsulation.

    Tunnel mode is mostly used to connect two networks, from router to router, while transport mode will be used for road-warriors, devices (laptop, iPhone), connecting to corporate network.

    L2TP over IPSec is similar to transport mode, connecting a remote device to a concentrator. The remote device can be however a router.

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