DMVPN Phase 3 Single Hub – EIGRP – Spoke example

Traffic Flow:

• Packet is sent from Spoke’s 1 network to Spoke’s 2 network via Hub (according to routing table)
• Hub routes packet to Spoke2 but in parallel sends back the NHRP Redirect message to Spoke1 containing information about suboptimal path to Spoke2 and tunnel IP of Spoke2
• Spoke1 then issues the NHRP Resolution request of Spoke’s 2 NBMA IP address to NHS with destination IP of Spoke’s 2 tunnel, this NHRP Resolution request is sent targeted to Spoke2 via NHS (according to routing table) – it is normal hop by hop NHRP forwarding process
• Spoke2 after receiving resolution request including NBMA IP of Spoke1 sends the NHRP Resolution reply directly to Spoke1 – Reply does not traverse the Hub!
• Spoke1 after receiving correct NBMA IP of Spoke2 rewrites the CEF entry for destination prefix – this procedure is called NHRP Shortcut
• Spokes don’t trigger NHRP by glean adjacencies but NHRP replies updates the CEF

DMVPN Phase 3 and EIGRP

• Advertise spoke’s connected routes
• Disable split horizon on hub (Spoke to Spoke prefix advertisement)
• Enable Next-hop-self feature

R2 Spoke configuration:

router eigrp 111
network 10.1.2.0 0.0.0.255
network 172.16.1.0 0.0.0.255

interface Tunnel0
ip address 172.16.1.2 255.255.255.0
no ip redirects
ip nhrp authentication gmlabs
ip nhrp map 172.16.1.1 10.149.1.1
ip nhrp map multicast 10.149.1.1
ip nhrp network-id 111
ip nhrp holdtime 60
ip nhrp nhs 172.16.1.1
ip nhrp registration timeout 30
ip nhrp shortcut
tunnel source Loopback0
tunnel mode gre multipoint
tunnel key 123
tunnel protection ipsec profile DMVPN_PROFILE
end

R3 Spoke configuration:

router eigrp 111
network 10.1.3.0 0.0.0.255
network 172.16.1.0 0.0.0.255
!
interface Tunnel0
ip address 172.16.1.3 255.255.255.0
no ip redirects
ip nhrp authentication gmlabs
ip nhrp map 172.16.1.1 10.149.1.1
ip nhrp map multicast 10.149.1.1
ip nhrp network-id 111
ip nhrp holdtime 60
ip nhrp nhs 172.16.1.1
ip nhrp registration timeout 30
ip nhrp shortcut
tunnel source Loopback0
tunnel mode gre multipoint
tunnel key 123
tunnel protection ipsec profile DMVPN_PROFILE
end
POD1_R3#