Why does this failure occur?

An engineer is troubleshooting a new DMVPN setup on a Cisco IOS router. After the show crypto isakmp sa command is issued, a response is returned of "MM_NO_STATE."

Why does this failure occur?
A . The ISAKMP policy priority values are invalid.
B. ESP traffic is being dropped.
C. The Phase 1 policy does not match on both devices.
D. Tunnel protection is not applied to the DMVPN tunnel.

View Answer

Answer: C

Explanation:

https://www.cisco.com/c/en/us/support/docs/security/dynamic-multipoint-vpn-dmvpn/111976-dmvpn-troubleshoot-00.html

The MMNOSTATE failure occurs when the ISAKMP policy priority values are not configured correctly on both devices. The ISAKMP policy priority values are used to determine the order in which the ISAKMP policies are applied. If the priority values do not match between the two devices, the ISAKMP tunnel may not be established correctly, resulting in the MMNOSTATE failure. To resolve this issue, the engineer should ensure that the ISAKMP policy priority values are configured correctly on both the router and the peer.