DMVPN Phase 2 Hub & Spoke – EIGRP example
Traffic Flow:
- Packet is intended to be sent from Spoke1 to Spoke2 network
- According to routing table Spoke’s2 network is known via its original next hop but it is marked in CEF as incomplete and next hop IP is marked simultaneously as CEF glean adjacency / punt (now, need to perform NHRP resolution) – the NBMA of next hop is unknown, so Spoke1 triggers NHRP resolution to NHS (including next hop of Spoke2, Source of its tunnel, it’s NBMA)
- In the same time first packet is routed via Hub based on RIB
- Similar thing is done by Spoke2 when it needs to send packet back to Spoke1
- NHS (Next hub self ) responds with NHRP resolution and then CEF is populated as complete and Spokes can communicate directly
DMVPN Phase 2 and EIGRP
- Advertise spoke’s connected routes
- Disable split horizon on hub (Spoke to Spoke prefix advertisement)
- Disable Next hop self feature
Hub:
conf t
!
router eigrp 100
network 20.1.1.0 0.0.0.255
network 172.16.1.0 0.0.0.255
!
interface Tunnel0
ip address 172.16.1.1 255.255.255.0
no ip redirects
no ip next-hop-self eigrp 100
ip nhrp authentication AVIU@OLU
ip nhrp map multicast dynamic
ip nhrp network-id 111
no ip split-horizon eigrp 100
no ip split-horizon
tunnel source Loopback0
tunnel mode gre multipoint
tunnel key 123
tunnel protection ipsec profile DMVPN_PROFILE
Spoke A :
conf t
!
router eigrp 100
network 20.1.2.0 0.0.0.255
network 172.16.1.0 0.0.0.255
!
interface Tunnel0
tunnel mode gre multipoint
Spoke B :
conf t
!
router eigrp 100
network 20.1.3.0 0.0.0.255
network 172.16.1.0 0.0.0.255
!
interface Tunnel0
tunnel mode gre multipoint
NOTE : The tunnel destination command need to be removed because of mGRE behavior: