DMVPN Phases

DMPVN Phases

• DMVPN Phase 1
• mGRE on hub and p-pGRE on spokes
• NHRP still required for spoke registration to hub
• No spoke-to-spoke tunnels
• Routing
• summarization/default routing at hub is allowed
• Next-hop on spokes is always changed by the hub
• DMVPN Phase 2
•  mGRE on hub and spokes
• NHRP required for spoke registration to hub
• NHRP required for spoke-to-spoke resolution
• Spoke-to-spoke tunnel triggered by spoke
• Routing
• Summarization/default routing at hub is NOT allowed
• Next-hop on spokes is always preserved by the hub
• Multi-level hierarchy requires hub daisy-chaining
• DMVPN Phase 3
• mGRE on hub and spokes
• NHRP required for spoke registration to hub
• NHRP required for spoke-to-spoke resolution
• When a hub receives and forwards packet out of same interface
• Send NHRP redirect message back to packet source
• Forward origin packet down to spoke via RIB 
• Routing
• Summarization/default routing at hub is allowed
• Results in NHRP routes for spoke-to-spoke tunnel
• With no-summary, NHO is performed for spoke-to-spoke tunnel
• Next-hop is changed from hub IP to spoke IP
• Next-hop on spokes is always changed by the hub
• Because of this, NHRP resolution is triggered by hub
• Multi-level hierarchy works without daisy-chaining
 
Reference
DMVPN_CONFIGURATION_CISCO_DOC 
DMVPN_INE_DMVPN_REVIEW