DMVPN Router Behind ASA - Need Help Please.


After reading many other discussions on this topic, it appears with the correct IOS and NAT-T enabled router, you can bring up DMVPN behind a NAT device.

I have attempted to complete this task, but I cannot even get phase 1 going for the DMVPN. The routing has been verified and I can ping the public IP's from the DMVPN routers. I am pretty sure the configurations for the routers are good, but question whether any additional NAT is required on the ASA.

Here is the topology:

DMVPN hub > ASA > Internet > ASA > DMVPN Branch

The ASA on the hub side is in our Data Center and is in production with several site-to-sites and DMZ traffic. The DMVPN devices is a Cisco 2921 and 1921. When I run a "debug crypto isakmp" on both routers, I see ISAKMP messages being sent on the branch DMVPN router ONLY. From the debug output it would appear phase 1 settings do not match but I have verified this. Nothing in the Hub and no hits on the ASA ACL's.

I have tried both the public IP's and the private IP's for the ACL on the ASA. I also did port forwarding in the ASA to port forward UDP ports to the DMPVN router as I was told I may need this.


I have attached the relevant configurations and can post more if needed.


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I see ISAKMP messages being sent on the branch DMVPN router ONLY.

This is normal for DMVPN - only the branch routers will initiate connections.

From your description, I assume that the GRE tunnel is going to be protected via IPSec.  You need to make sure you're allowing UDP 500 and UDP 4500 in both directions.

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Pete LongTechnical ConsultantCommented:
To be honest, Id bring up the DMVPN tunnel over GRE, then protect it with IPSEC, then you are only troubleshooting one technology at a time.
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