DMVPN Phase 2 Basic Configuration

This topic is to discuss the following lesson:

Thanks for the good explanation Rene. I am using Cisco 7200 with IOS version 12.4(24g) but show dmvpn command is not working. Other configuration commands to setup DMVPN worked.

R1#show dmvpn
         ^
% Invalid input detected at '^' marker.

R1#

Hello Abhishek

It seems that this command is not available in your IOS version. You can see from the following Cisco CLI reference, that the command was introduced in the T train of code and not in the mainline which is your IOS version.

Even so, this is simply a show command that conveniently displays the components of the topology. You can still obtain the same information with a variety of other show commands such as those indicated in the following Cisco document:


Note this document was published before the introduction of of the show dmvpn command.

I hope this has been helpful!

Laz

Hello Rene

Hope you doing great.

On show dmvpn output I see Attrb --> S for Spokes routers meaning that the NBMA peer Address is learned Statically.

Shouldn’t be Attrb --> S like the Hub router?

Thank you in advance!

Regards,
Victor

Hello Victor

When you use DMVPN with NHRP in the configuration found in the lesson, on each spoke you use the following command:

ip nhrp map <tunnel address> <hub NBMA address>

This creates a static peer address, and that’s why you see the “S” indicator on the spoke router. This is considered a statically configured NBMA peer address.

On the hub, however, you have no such configuration. The hub is configured to accept NHRP requests to dynamically add the addresses of the spokes. For this reason, on the Hub, you will see the “D” designation that these are dynamically learned addresses.

You can, however, configure static spoke addresses on the hub if you like, but this defeats the purpose of the simplicity of implementation and the scalability of DMVPN.

I hope this has been helpful!

Laz

I hope this has been helpful!

Hi Laz,

Please explain the commands by taking example of IPs we used in n/w topology for DMVPN.

  1. ip nhrp map 172.16.123.1 192.168.123.1
  2. ip nhrp map multicast 192.168.123.1
    3)ip nhrp nhs 172.16.123.1 ( why are we using tunnel address here, it should be
    public ip)
  3. diff b/w ip nhrp map multicast dynamic and ip nhrp map multicast
    192.168.123.1
  4. ip nhrp mode multipoint command instead of tunnel destination address.
    we know tunnel destination command is being used to specify destination
    address but multipoint mean it can be both source and destination ip. so how
    can we replace tunnel destination command by ip nhrp mode multipoint
    command?

Hello Pradyumna
For the first four points of your question, these commands are explained in detail in the following lesson:


Also keep in mind that the ip nhrp nhs command must indicate the tunnel IP as configured, and not the public IP.

For your last question, the primary difference between Phase1 and Phase2 is that in Phase2 you can have spoke to spoke communication. It is the multipoint mode that is configured on the spokes that enables this specific feature.

I hope this has been helpful!

Laz