Understanding "MM_NO_STATE" Error in Cisco DMVPN Setup

B.

When configuring a DM VPN on a Cisco IOS router, the "MM_NO_STATE" response is an indication that the Internet Security Association and Key Management Protocol (ISAKMP) state is not present. This indicates a failure in the negotiation process between the two endpoints of the VPN connection.

To resolve this issue, the engineer must investigate the possible causes for this failure. Some of the potential causes and their solutions are as follows:

A. Invalid ISAKMP Policy Priority Values: If the ISAKMP policy priority values are not set correctly, the routers will not be able to negotiate the VPN connection. The engineer should verify that the policy priority values are correct on both devices and that they match.

B. ESP Traffic is being dropped: If the encrypted security payload (ESP) traffic is being dropped by a firewall or other network security device, the VPN connection will fail. The engineer should ensure that the necessary ports and protocols are allowed through any firewalls or security devices that are present on the network.

C. Phase 1 Policy Does Not Match on Both Devices: The ISAKMP phase 1 policy must match on both devices for the VPN connection to be established. If the phase 1 policy does not match, the VPN connection will fail. The engineer should verify that the phase 1 policy matches on both devices.

D. Tunnel Protection is not Applied to the DM VPN Tunnel: If tunnel protection is not applied to the DM VPN tunnel, the VPN connection will fail. The engineer should ensure that tunnel protection is applied to the DM VPN tunnel.

In summary, the "MM_NO_STATE" response when issuing the show crypto isakmp sa command indicates that the ISAKMP state is not present, and the VPN connection has failed to establish. The engineer must investigate the possible causes and resolve them to establish the VPN connection successfully.