Exam 300-410 topic 1 question 326 discussion

From the Cisco page that HungarianDish_111 shared below: Prerequisites for Dynamic Multipoint VPN (DMVPN) Before a multipoint GRE (mGRE) and IPsec tunnel can be established, you must define an Internet Key Exchange (IKE) policy by using the crypto isakmp policy command. For the NAT-Transparency Aware enhancement to work, you must use IPsec transport mode on the transform set. Also, even though NAT-Transparency can support two peers (IKE and IPsec) being translated to the same IP address (using the User Datagram Protocol [UDP] ports to differentiate them [that is, Peer Address Translation (PAT)]), this functionality is not supported for DMVPN. All DMVPN spokes must have a unique IP address after they have been NAT translated. They can have the same IP address before they are NAT translated. To enable 2547oDMPVN--Traffic Segmentation Within DMVPN you must configure multiprotocol label switching (MPLS) by using the mpls ip command.

According to this it's A, C

What makes me choose C is that you do not need to ping that device for build UP the phase 1 ike tunnel and then the CHILD_SA what you need is to make intresting traffic for the VPN. After that you should have the tunnel UP and you can do other traffic like http/tcp/udp or other type of traffic that you need. So I will go with A and C the other one do not make much sense

I'm going for A and C based on the documentation provided in the comments below. For B, if we NAT the ip address, the original public IP addresses don't have to be pingable. For the NAT-Transparency Aware enhancement to work, you must use IPsec transport mode on the transform set. Also, even though NAT-Transparency can support two peers (IKE and IPsec) being translated to the same IP address (using the User Datagram Protocol [UDP] ports to differentiate them [that is, Peer Address Translation (PAT)]), this functionality is not supported for DMVPN. All DMVPN spokes must have a unique IP address after they have been NAT translated. They can have the same IP address before they are NAT translated.

I vote for AB, because for configuring DMVPN, you don't need the "mpls ip" command.

A. Before a multipoint GRE (mGRE) and IPsec tunnel can be established, define an Internet Key Exchange (IKE) policy by using the crypto isakmp policy command. Correct: Defining an IKE policy is essential for establishing secure communication between routers. The IKE policy is used to configure the parameters for IKE negotiations, which are necessary for setting up IPsec encryption. B. The Public IP’s of the routers should be able to ping each other. Correct: The routers need to be able to reach each other over the public Internet or other IP network. This connectivity is crucial for establishing the initial DMVPN connection and ensuring that the routers can communicate.

A & C are correct

The question is clearly taken from here, as DUBC89x pointed out, and so, I agree on the answers "A", "C". https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/sec_conn_dmvpn/configuration/15-mt/sec-conn-dmvpn-15-mt-book/sec-conn-dmvpn-dmvpn.html#GUID-D8F6839F-D735-4C8E-A199-602CDD8F7DD0 However: IPsec is only optional for basic DMVPN tunnel configuration. https://networklessons.com/cisco/ccie-routing-switching/dmvpn-over-ipsec Of course, I can't imagine using DMVPN without IPsec, still it is a tricky question, because IPsec is not needed for the DMVPN tunnel establishment. Also, normally I would check reachability via the WAN/public IPs before setting up the tunnel. So, I would not say that "B" is wrong.

Given answer is correct. "Prerequisites for Dynamic Multipoint VPN (DMVPN) Before a multipoint GRE (mGRE) and IPsec tunnel can be established, you must define an Internet Key Exchange (IKE) policy by using the crypto isakmp policy command. For the NAT-Transparency Aware enhancement to work, you must use IPsec transport mode on the transform set. Also, even though NAT-Transparency can support two peers (IKE and IPsec) being translated to the same IP address (using the User Datagram Protocol [UDP] ports to differentiate them [that is, Peer Address Translation (PAT)]), this functionality is not supported for DMVPN. All DMVPN spokes must have a unique IP address after they have been NAT translated. They can have the same IP address before they are NAT translated. To enable 2547oDMPVN--Traffic Segmentation Within DMVPN you must configure multiprotocol label switching (MPLS) by using the mpls ip command." https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/sec_conn_dmvpn/configuration/15-mt/sec-conn-dmvpn-15-mt-book/sec-conn-dmvpn-dmvpn.html#GUID-D8F6839F-D735-4C8E-A199-602CDD8F7DD0