Which condition prevents the establishment of a DMPVN tunnel between two spokes?
A. HSRP is enabled on the spoke devices
B. IPsec is enabled on the spoke devices
C. the two spokes are behind different PAT devices
D. the two spokes have different tunnel keepalive settings.
In DMVPN networks, spoke-to-spoke tunneling is limited to spokes that are not behind the NAT device. If
one or both spokes are behind a NAT device, a spoke-to-spoke tunnel cannot be built to or from the NAT
device because it is possible for the spoke-to-spoke tunnel traffic to fail or be lost “black-holed” for an extended
period.
C
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/sec_conn_dmvpn/configuration/xe-16-10/sec-conn-dmvpn-xe-16-10-book/sec-conn-dmvpn-dt-spokes-b-nat.pdf
“• If one spoke is behind one NAT device and another different spoke is behind another NAT device, and
Peer Address Translation (PAT) is the type of NAT used on both NAT devices, then a session initiated
between the two spokes cannot be established.”
C. the two spokes are behind different PAT devices