DMVPN Phase 2 RIP Routing

[lagapidis (Lazarus Agapidis)]

Hello Pradyumna

@pradyumnayadavgla

1)I am getting confused, actually still has not got in which phase NHRP registration, resolution and reply message will be sent?

The section that describes NHRP and the three phases of DMVPN in the following lesson show the differences between the phases and how NHRP functions:

Introduction to DMVPN

@pradyumnayadavgla

2. In phase 2 debugging on Spoke 1 and Spoke 2 has got me confused, even I am unable to understand why are we resolving NBMA address of hub when spoke 1 looking for NBMA address of Spoke 2?, and how spoke 2 known NBMA address of spoke 1 tunnel int in message one and other message until it sends nhrp request?

As soon as the network is up, if you do a show dmvpn on the spokes, you will only find that the hub is registered. So the NHRP cache does not include the entries of the other spokes. Even though Spoke 1 has a routing entry for the destination, it does not have an NHRP entry. For this reason, an NHRP resolution request is sent to the hub. The hub responds with the IP address of the other spoke, and the NHRP entry is installed in the cache. From there on, direct spoke to spoke communication can take place. This process is detailed in this section of the Introduction to DMVPN lesson.

@pradyumnayadavgla

3. Suppose this time Spoke 1 started communication and for how long this
   communication valid is and when spoke 2 will initiate same process of
   communication with spoke 2 mean I want to know which one will be the
   initiator, when and how?

Regardless of which router starts the communication, the NHRP entries are placed within both spokes. You can see this at the end of the lesson, where both spokes have each other’s registration. The registrations time out after 40 minutes of no traffic between them, but this value can be changed using the ip nhrp registration timeout command. More about that command can be found here.

@pradyumnayadavgla

4. Also confused how packet forming and which header is removing at which
   router from spoke to spoke communication mean whole encapsulation and
   decapsulation in DMVPN network during full spoke to spoke communication.

You can find out more about this at the following post:

DMVPN Phase 1 RIP Routing

Hello Pradyumna The encapsulation is exactly the same as that found with normal GRE. Taking it step by step from the beginning: Spoke1 creates an ICMP message and encapsulates it into an IPv4 packet with a source and destination address of 2.2.2.2 and 3.3.3.3 respectively. These are the IP addresses of the source of the ICMP echo, and the destination host from which a reply is expected. This IPv4 packet is then encapsulated with a GRE header which simply tells the router that a tunnel is …

I hope this has been helpful!

Laz