19. DMVPN Tunnels

Question 1

What are the 5 NHRP message types in DMVPN?

Answer 1

• Registration
• Resolution
• Redirect
• Purge
• Error

Question 2

Why is the DMVPN registration message used?

Answer 2

Sent by a NHC to the NHS to provide a spokes NBMA information. Also specifies the time the registration should be maintained.

Question 3

Why is the DMVPN resolution message used?

Answer 3

Used to locate and provide the address resolution information of the egress router towards the destination. The resolution request is sent during the actual query

Question 4

Why is the DMVPN Redirect message used?

Answer 4

Used in DMVPN phase 3. Allows a intermediate router to notify the encapsulator that a specific network can be reached by using a more optimal path (spoke-to-spoke tunnel).

Question 5

Why is the DMVPN purge message used?

Answer 5

To remove a cached NHRP entry. Typically sent from NHS to NHC to inform that a mapping for an address is not valit anymore.

Question 6

What is NHRP?

Answer 6

Network Hop Resolution Protocol that provides address resolution to hosts or networks for a NBMA network.

Question 7

What are the supported overlay protocols in DMVPN?

Answer 7

• IPv4
• IPv6
• MPLS

Question 8

What does the command ip nhrp redirect do?

Answer 8

It checks the flow of packets on the tunnel interface and sends a redirect message to the source spoke router when it detects packets hairpinning out if the DMVPN cloud.

Question 9

Where is the command ip nhrp registration no-unique used for?

Answer 9

To ignore the request of the NHC to have the NHS to keep it’s NBMA address