DMVPN Phase-2 Implementation
Introduction
Overlay Configuration
Routing Protocol Configuraton
Verification
Conclusion
Introduction
- The disadvantage of phase 1 is that there is no direct spoke to spoke tunnels. In phase 2, all spoke routers use multipoint GRE tunnels so we do have direct spoke to spoke tunneling.
- When a spoke router wants to reach another spoke, it will send an NHRP resolution request to the hub to find the NBMA IP address of the other spoke.
- There are two requirements to make spoke to spoke tunnels work:
- Spoke routers need to have a route for the network that they are trying to reach.
- The next hop IP address of the route has to be the remote spoke.
- The configuration of DMVPN phase 1 and 2 is similar except for two key items:
- The spoke routers will now use multipoint GRE interfaces instead of point-to-point GRE interfaces.
- We don’t configure a manual destination anymore on the spoke routers.
Lab Topology
Assuming that all routers are having Underlay configuration. Here are the steps for Overlay configuration:
R1 configuration
R1(config)# interface Tunnel 0
R1(config-if)# ip address 192.168.1.1 255.255.255.0
R1(config-if)# tunnel mode gre multipoint
R1(config-if)# tunnel source Ethernet0/0
R1(config-if)# ip nhrp authentication Cisco@123
R1(config-if)# ip nhrp map multicast dynamic
R1(config-if)# ip nhrp network-id 1
R1(config-if)# exit
R2 configuratoin
R2(config)# interface tunnel 0
R2(config-if)# ip address 192.168.1.2 255.255.255.0
R2(config-if)# ip nhrp authentication Cisco@123
R2(config-if)# ip nhrp map 192.168.1.1 1.1.1.1
R2(config-if)# ip nhrp map multicast 1.1.1.1
R2(config-if)# ip nhrp network-id 1
R2(config-if)# ip nhrp nhs 192.168.1.1
R2(config-if)# tunnel source Ethernet0/0
R2(config-if)# tunnel mode gre multipoint
R2(config-if)# exit
R3 Configuration
R3(config)# interface tunnel 0
R3(config-if)# ip address 192.168.1.3 255.255.255.0
R3(config-if)# ip nhrp authentication Cisco@123
R3(config-if)# ip nhrp map 192.168.1.1 1.1.1.1
R3(config-if)# ip nhrp map multicast 1.1.1.1
R3(config-if)# ip nhrp network-id 1
R3(config-if)# ip nhrp nhs 192.168.1.1
R3(config-if)# tunnel source Ethernet0/0
R3(config-if)# tunnel mode gre multipoint
R3(config-if)# exit
Phase-2 Routing Protocol (Eigrp) Configuration
R1(config)# router eigrp 1
R1(config-router)# network 10.10.1.0 0.0.0.255
R1(config-router)# network 192.168.1.0
R1(config-router)# no auto-summary
R1(config-router)# exit
R1(config)# int tunnel 0
R1(config-if)# no ip split-horizon eigrp 1
R1(config-if)# no ip next-hop-self eigrp 1
R1(config)# end
R2(config)# router eigrp 1
R2(config-router)# network 10.10.2.0 0.0.0.255
R2(config-router)# network 192.168.1.0
R2(config-router)# no auto-summary
R2(config-router)# exit
R3(config)# router eigrp 1
R3(config-router)# network 10.10.3.0 0.0.0.255
R3(config-router)# network 192.168.1.0
R3(config-router)# no auto-summary
R3(config-router)# exit
Verification
Conclusion:
A significant drawback of DMVPN Phase 2 is its routing limitations, particularly when scaling to a large number of spokes. Each spoke needs to maintain routing information for all other spokes, leading to large routing tables and increased processing overhead on the hub. Additionally, spoke-to-spoke traffic in Phase 2 often relies on the hub as an intermediary, introducing potential latency and reduced performance. The drawbacks of DMVPN Phase 2 is over come by DMVPN Phase 3, which we are going to discuss in another article.
............................................................................................ Thank you very much..! ...........................................................................
1 Comment
