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Sonicwall TZ210 DH group reverts from 2 to 1

Posted on 2013-11-21
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Last Modified: 2013-12-11
My sonicwall TZ210 periodically changes the DH group from 2 to 1 on one of the VPN connections. Is there a reason why?
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Question by:penguins_rule
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by:Ugo Mena
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What is the client using to connect to the SonicWall VPN?

Do you have "Enable Perfect Forward Secrecy" enabled?
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by:diverseit
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Hi penguins_rule,

Upgrade the firmware and retest.
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by:penguins_rule
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Client has a Cisco ASA 5505
Enable Perfect Forward Secrecy is not enabled
Current firmware version is SonicOS Enhanced 5.5.1.0-5o

It's not convenient to upgrade the firmware unless it is really necessary.
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by:Ugo Mena
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Are you using Certificates or a preshared secret for IKE Policy?

Do you know what version ASA release client is running?

In general, I think you have an IKEv2 policy that is falling back to IKEv1 due to an IKEv2 incompatible device...
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by:penguins_rule
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The connection works fine for several weeks at a time.
Then the DH Group reverts back to 1 on the Sonicwall. The client using the Cisco ASA 5500 cannot connect until the Sonicwall is changed back to DH group 2

Using IKE preshared key
ASA release client is not readily attainable
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Ugo Mena earned 250 total points
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I was under the assumption that your Site to Site VPN was still working through the DH Group change and figured it might be an IPSEC negotiated fallback to IKEv1.
 
After looking into release notes for your specific firmware version, I will second diverseit's recommendation to upgrade the firmware.

Version 5.9.0.1-100o is the current version for TZ200 series, released Sept 5, 2013.

Version 5.5.1.0-5o was released Oct 5, 2009 and was determined to have a variety of Known Issues with VPN's specifically.

Nothing calls out your DH group change issue outright, but it seems like the most likely cause at this point is the firmware version.
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by:diverseit
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It's not convenient to upgrade the firmware unless it is really necessary.
It's not only a Best Practice to keep your firmware up-to-date but it's a very simple process even in a production environment - total downtime 1-2m - do it over lunch. The current firmware release is 5.9.0.2-107o - you should backup your settings and upgrade to that. The reason to do this is it fixes any bugs and/or compatibility issues that may exist - your firmware is heavily out of date.

Are you seeing anything in the logs talking about IKE Responder: IKE proposal does not match (Phase 1), or IKE Responder: IPSec Proposal does not match (Phase 2)?

The initiating SonicWALL sent an IPSec proposal that does not match the responding SonicWall during Phase 2 negotiations. There should be an additional error message in the responder log specifying the proposal item that did not match.

Sometimes you will see this error when you have a site-to-site VPN in Aggressive mode. In this setup, it usually means the name of the VPN SA was not the same as the Unique Firewall Identifier (UFI) of the device on the other side. Each side must be the same as the UFI of the device on the opposite end.

Let me know how it goes!
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by:penguins_rule
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thanks for your help. I will schedule an upgrade to the firmware. it may take a few weeks, i will post how it goes.
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by:diverseit
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No problem...we'll be here for you!
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by:penguins_rule
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upgraded the firmware to the current version. On the reboot with current firmware, the DH group was changed from 2 to 1. I will have to wait and see if it changes again.
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by:diverseit
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That is nothing to worry about on the onset. Sometimes for compatibility reasons settings slightly change especially when going from deprecated firmware versions to new core releases.

I'd change it all to DH2 and then restart the SonicWALL. Everything should be OK thereafter.

Let me know how it goes!
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