Cisco Router VPN main mode for client

Posted on 2015-02-14
Last Modified: 2015-02-19
Our company failed an audit because ike-scan says that we have an open aggressive ike connection visible externally. The auditors proposal is to fix the handshake from aggressive to main mode. The problem is, I'm not sure how to set it up on VPN Client using shrew soft. Is there a way you can advise how to fix and get rid of the problem below?

Something like this:
a.b.c.10  Aggressive Mode Handshake returned HDR=(CKY-R=353da776bbb4b996)
SA=(Enc=3DES Hash=MD5 Group=2:modp1024 Auth=PSK LifeType=Seconds LifeDuration=28
800) VID=12f5f28c457168a9702d9fe274cc0100 (Cisco Unity) VID=afcad71368a1f1c96b86
96fc77570100 (Dead Peer Detection v1.0) VID=c0fa006bbbb5b99678f8a0fa93809964 VID
=09002689dfd6b712 (XAUTH) KeyExchange(128 bytes) ID(Type=ID_IPV4_ADDR, Value=a
.b.c.10) Nonce(20 bytes) Hash(16 bytes)
a.b.c.77  Notify message 14 (NO-PROPOSAL-CHOSEN) HDR=(CKY-R=36431b96ca6a9cf4)
a.b.c.105 Aggressive Mode Handshake returned HDR=(CKY-R=1ecbf70ceb9f629b)
SA=(Enc=3DES Hash=MD5 Group=2:modp1024 Auth=PSK LifeType=Seconds LifeDuration=28
800) VID=09002689dfd6b712 (XAUTH) VID=afcad71368a1f1c96b8696fc77570100 (Dead Pee
r Detection v1.0) VID=12f5f28c457168a9702d9fe274cc0100 (Cisco Unity) VID=eb0c501
1eb9e629b323f3948e404dff2 KeyExchange(128 bytes) ID(Type=ID_FQDN, Value=pix01. Nonce(20 bytes) Hash(16 bytes)
a.b.c.130 Unexpected IKE payload returned: Delete Notification=(Type=INVALID-EXCHANGE-TYPE, SPI=, Data=)

Ending ike-scan 1.9: 256 hosts scanned in 42.905 seconds (5.97 hosts/sec).  2 re
turned handshake; 1 returned notify
Question by:SuperRoot
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Author Comment

ID: 40610367
I'm basically recreating the whole config from the scratch just unsure how.
LVL 95

Expert Comment

by:John Hurst
ID: 40610380
I do not know the settings for your router.

IKE with Preshared Key
Phase 1 DH Group 2
Phase 1 3DES
Phase 1 SHA1
Phase 2 the same
PFS not enabled
Aggressive Mode not enabled (so Main mode is used)
NAT Traversal enabled.

You would have other settings but I checked all client tunnels and Aggressive Mode is not ever enabled.

Perhaps you can match the above to your settings.

Author Comment

ID: 40610400
That's what I have currently:
crypto isakmp policy 3
 encr 3des
 authentication pre-share
 group 14
 lifetime 28800
crypto isakmp keepalive 10

crypto ipsec transform-set PDBENC esp-3des esp-sha-hmac

Is this good?
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LVL 95

Expert Comment

by:John Hurst
ID: 40610403
Looks comparable to my settings. Make sure Main Mode is set or Aggressive Mode is not checked.
LVL 95

Expert Comment

by:John Hurst
ID: 40610404
Also, you may need to use Aggressive Mode with remote software clients. I have to do that because the remote end is not fixed at all. I should think your auditor would understand that.

So site-to-site is all Main Mode and site-to-client is Aggressive Mode for the client software.

Author Comment

ID: 40610481
I talked to my auditor. He said there's no security in an aggressive mode. All routers have capability to setup IKEv2 with main mode. Question is, how do we do that on cli?

Accepted Solution

Daniel Sheppard earned 250 total points
ID: 40610527
IKEv2 for Client VPN's is only available with FlexVPN (Anyconnect and G2 ISRs/ASRs) or Cisco ASAs.

What router do you have?

Edit:  Just saw you taged it with Cisco 1181 (Assuming you mean 1811).  You cannot use FlexVPN on this product.  Your next best would be to perhaps move to WebVPN and use SSL, however that too has attack vectors.  If you want to get your audit up, you will need to move to a different platform, either that or accept your current standing.

If you want main mode, you have to move to certs instead of PSK.
LVL 95

Expert Comment

by:John Hurst
ID: 40610749
He said there's no security in an aggressive mode <-- I do not think that is correct at all. Aggressive is needed (I think) on remote access software clients.
LVL 95

Assisted Solution

by:John Hurst
John Hurst earned 250 total points
ID: 40613170
Please read the article below:

It says that Aggressive Mode is not as secure in Phase 1 communication because that one exchange is in clear text.  The resulting tunnel is NOT in clear text or insecure. Only for a split second is there is a lesser security.

It also says Aggressive mode is used for remote application software (which I said above) and when dynamic addressing is used (which I said above).

So the resulting tunnel Main and Aggressive is the same and there is only a split second when one Phase is insecure. IPsec change the security key on an ongoing basis from the key supplied.

I hope this helps.

Author Comment

ID: 40613258
Yeah I looked at it. I can't setup main mode. It doesn't work on my old Cisco router though I manage to increase the encryption to group 14, sha256, and aes256. This way it has the highest form of encryption. I left aggressive running. I tested the Ike tester and now I get different error. I'll ask my auditor what he thinks and go from there. Thanks for your help. I'll update you all on Wednesday.
LVL 95

Expert Comment

by:John Hurst
ID: 40613263
I think your auditor is overdoing it. There is no real issue with Aggressive Mode in a dynamic, remote installation. Some hacker would have to sit on the remote site at the split second the user transmits Phase 1. The odds are really tiny.

The encryption I gave you is reasonable. Your increased encryption is probably better but needs more hardware and remote application horsepower to keep up.

I have had Main Mode site to site tunnels up at clients for nearly 15 years (OS and security upgraded along the way) and zero transgressions.

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