FlexVPN: AnyConnect IKEv2 Remote Access: Common Mistake

The issue came to my attention, after reading cisco article on IKEv2: 

https://www.cisco.com/en/US/docs/ios-xml/ios/sec_conn_ikevpn/configuration/15-1mt/Configuring_Internet_Key_Exchange_Version_2.html

Under the proposal section it states:

>  “Manually configured IKEv2 proposals must be linked with an IKEv2 policy; otherwise, the proposals are not used in the negotiation”

consequently when a proposal is manually configured, this must be called/linked to a policy for example:

> *> Crypto IKEv2 proposal nwlesson_Proposal*

> *> {Encryption Algorithm} e.g aes-cbc256 etc*

> *> {Integrity Algorithm} any hash of your choice e.g SHA etc *

> *> {Pseudo-Random function (PRF)} The PRF algorithm is the same as integrity algorithm, subesquently this does not to separately configured*

> {Diffie-Hellman(DH) Group}

> >

I discovered yesterday in the lab, **if** you want this proposal to be utilised in the IKEv2 negotiation it MUST be called/linked by a policy for example:

> *Crypto IKEv2 Policy nwlesson_Policy*

> *proposal nwlesson_Proposal (our proposal we configured above)*

During a friday night dinner out with the family. I kept thinking, what happens if we don’t link the proposal to a policy? 

Subsequently from 10pm untill 1am in the lab, I tested this theory. The configured proposal(encryption, Integrity, PRF algorithm and DH group) is not utilised in the SA_INIT exchange of the IKEv2 negotiation, if there isn’t a policy!

subsequently the question becomes, what proposal is being utilised if the one we configured isn’t being used in the exchange? 

The answer: the default proposal!(remember smart defaults?)

You will notice there is no policy that links the proposal, just a authorization policy which technically is completely different. Subsequently we are not using those proposal declared in the tutorial for the negotiation we are simply using **default** values provided by IOS:

in order to utilise the proposa(IKEV2_PROPOSAL)l that was declared in the lesson we must include the following in the tutorial guide:

> *Crypto IKEv2 Policy nwlesson_Policy*

> *proposal  IKEV2_PROPOSAL*


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