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RS0015 - NHRP Phase 1

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The video looks at Next Hop Resolution Protocol (NHRP) Phase 1 with Hub-and-Spoke topology and explains the differences from point-to-point GRE tunnel. NHRP is the basis of widely-used DMVPN. Without the IPSec encryption in DMVPN, we are able see the actual NHRP packets in action, which helps to understand how the protocol operates (ie. Spoke Registration Request/Reply). We will analyze these packets in Wireshark. 

Topic includes
  • NHRP Phase 1 - Hub-and-Spoke
  • NHRP Registration Request/Reply
  • Next Hop Server (NHS) maintains dynamic mappings between logical and physical endpoint addresses learnt at the time of endpoint registration
  • Next Hop Client (NHC) queries NHS for a physical IP address of the other spoke to build spoke-to-spoke tunnel
  • Registration message is sent every one-third of NHRP holdtime by default unless specified
  • NHRP Phases
    • Phase 1 – Hub-and-Spoke only
    • Phase 2 - Spoke-to-Spoke. Each spoke maintain next-hop information of the other spokes
    • Phase 3 – Spoke-to-Spoke with enhancement (Hierarchical Topology, Route Summarization)

About Author

Metha Cheiwanichakorn, CCIE#23585 (RS, Sec, SP), is a Cisco networking enthusiast with years of experience in the industry. He is currently working as a consulting engineer for a Cisco partner. As a founder of and an instructor at, Metha enjoys learning and challenges himself with new Cisco technologies.


great video...thanks

i am running the configuration in gns3 so i wonder the switch, what kind or should i use a router instead ?

Last we checked GNS3 still does not have L3 switch. There might be a switch module on the router but even so it still L2 so you will need to use router as an L3 device for the config.

if i use L3 devices, do i need to perform any routing on that device

You may need routing if you don't use directly connected interfaces on Hub and Spoke. 

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