undestanding ipsec, isakmp

Unanswered Question
Mar 11th, 2007

I have a few questions about VPN and maybe someone can help me understand a little better:

ISAKMP is phase 1 which builds the tunnel,matching endpoints correct?

IPSEC is phase 2 which encrypts the traffic after the tunnel has been built and is active, correct?

The router then will not even attemp to encrypt the data and send it across the tunnel, unless phase 1 is working, correct?

The crypto isakmp policy is phase 1,

and the transform set is phase 2, is this correct?

Does the encryption in the isakmp policy have to match the transform set at all (3des, sha)or can you have aes in phase1, 3des in phase2?

I guess I don't understand about how the transform set is made up and why it is made up the way it is with multiple components:

esp-3des esp-sha-hmac

why does the crypto map refernece ipsec-isakmp (both of them)?

Since the crypto map applies an access-list to encrypt the data in the list, this is part of ipsec, phase 2, is this correct?

I have this problem too.
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kaachary Mon, 03/12/2007 - 03:06

Isakmp Phase 1 comprises of :

1: Iskamp policies

2: Iskamp key

IPsec Phase 2 comprises od :

1: Crypto Map (Crypto ACL, phase 2 lifeitme etc)

2: Transform set

crypto map ipsec-iskamp means IKE will be used for building SA.

The other method when IKe is not used is called "ipsec-manual" .


Isakmp policy decides the type of encryption, hashing and authentication method used for IKE negotiation. And transform set defines, the same parameters for actual data traffic.

They are not inter related. Trnasform set parameters can be different from ISAKMP policy parmaeters.

I hope it answers your questions.

*Please rate if helped.



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