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Dual DMVPN cloud with OSPF routing protocol implemented
Dual Cloud DMVPN failover solution is the most reliable way to achieve reachability in any case of failure. If one of the routers get fail we still have another one, if one of the ISPs links has died we have the second one. In the scenario I assumed there are only 2 Hubs and 2 Spokes but this solution is very well scalable.
Implementing Dual Hub is not hard, but when you are going to implement its with OSPF protocol then the challenge is getting more demanding. If you would choose EIGRP then the case is simple, you need to use “no ip split horizon”, “ip nhrp shortcuts” and “ip nhrp redirects” on the hubs. You may also easily manipulate which hub will be prefered by manipulating the EIGRP metrics .Before I go over configuration I would like to mention about a couple of things that we have to remember about, during implementation, then whole implementation will go seamlessly.
In regard to Areas in conjunction with Hub and Spokes you will have 2 choices:
1. Area0 behind the hubs, spokes and DMVPN tunnels in different area
2. Area0 over DMVPN tunnels and Hubs and different areas on each of the spokes
When you are going to use OSPF you also need to remember about this :
1. Configuring OSPF network type as Broadcast is the best option
2. Set tunnels type as multi GRE
3. Remember about matching timers, MTU, if you use IPSec decrease MTU to 1400 and MSS to 1360 at least to avoid packets defragmentation
4. You may set up Area with Spokes as Stubby or Totally Stubby in order to limit LSA type 3, 4 and 5 flooding
5. When you implementing OSPF via DMVPN as a non broadcast network, you have to establish neighberhood manually
6. ONLY hubs may be Desginated Routers, so you have to set their priority to something higher then 0, additionally the hub with higher priority will be the DR the second one the backup DR.
Now, let’s go over our lab
Hub1
interface Tunnel0
description PRIMARY CLOUD
bandwidth 1000
ip address 192.168.0.1 255.255.255.0
ip nhrp authentication itbundle
ip nhrp map multicast dynamic
ip nhrp network-id 1
tunnel key 1
ip ospf network broadcast
ip ospf hello-interval 1
ip ospf priority 1
ip ospf 1 area 1
tunnel source 1.1.1.1 255.255.255.0
tunnel mode gre multipoint
Hub2
interface Tunnel0
description SECONDARY CLOUD
bandwidth 1000
ip address 172.16.0.2 255.255.255.0
ip nhrp authentication itbundle
ip nhrp map multicast dynamic
ip nhrp network-id 2
tunnel key 2
ip ospf network broadcast
ip ospf hello-interval 1
ip ospf priority 2
ip ospf 1 area 1
tunnel source 2.2.2.2 255.255.255.0
tunnel mode gre multipoint
Spoke1
interface Tunnel0
description PRIMARY CLOUD
bandwidth 1000
ip address 192.168.0.3 255.255.255.0
ip nhrp authentication itbundle
ip nhrp map 192.168.0.1 1.1.1.1
ip nhrp network-id 1
tunnel key 1
ip nhrp nhs 192.168.0.1
ip ospf network broadcast
ip ospf hello-interval 1
ip ospf priority 0
ip ospf 1 area 1
tunnel source 3.3.3.3 255.255.255.0
tunnel destination 1.1.1.1
tunnel mode gre multipoint
interface Tunnel1
description SECONDARY CLOUD
bandwidth 1000
ip address 172.16.0.3 255.255.255.0
ip nhrp authentication itbundle
ip nhrp map 172.16.0.2 2.2.2.2
ip nhrp network-id 2
tunnel key 2
ip nhrp nhs 172.16.0.2
ip ospf network broadcast
ip ospf hello-interval 1
ip ospf priority 0
ip ospf 1 area 1
tunnel source 3.3.3.3 255.255.255.0
tunnel destination 2.2.2.2
tunnel mode gre multipoint
Spoke2
interface Tunnel0
description PRIMARY CLOUD
bandwidth 1000
ip address 192.168.0.4 255.255.255.0
ip nhrp authentication itbundle
ip nhrp map 192.168.0.1 1.1.1.1
ip nhrp network-id 1
tunnel key 1
ip nhrp nhs 192.168.0.1
ip ospf network broadcast
ip ospf hello-interval 1
ip ospf priority 0
ip ospf 1 area 1
tunnel source 3.3.3.3
tunnel destination 1.1.1.1
tunnel mode gre multipoint
interface Tunnel1
description SECONDARY CLOUD
bandwidth 1000
ip address 172.16.0.4 255.255.255.0
ip nhrp authentication itbundle
ip nhrp map 172.16.0.2 2.2.2.2
ip nhrp network-id 2
tunnel key 2
ip nhrp nhs 172.16.0.2
ip ospf network broadcast
ip ospf hello-interval 1
ip ospf priority 0
ip ospf 1 area 1
tunnel source 4.4.4.4
tunnel destination 2.2.2.2
tunnel mode gre multipoint