DMVPN Phase 2 Basic Configuration

In the first lesson about DMVPN we discussed the basics of multipoint GRE and NHRP. The second lesson was a basic configuration of DMVPN phase 1. This time i’ll explain how you can configure DMVPN phase 2. Once we have a basic configuration then we can try to run RIP, EIGRP, OSPF and BGP on top of it.

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.

That’s it, those two changes make the difference between running DMVPN phase 1 or 2.  Let’s take a look at the configuration, here’s the topology we will use:

dmvpn-example-topology

Above we have one hub router and two spoke routers. We use 192.168.123.0/24 as the underlay network and 172.16.123.0/24 as the overlay network.

Configuration

In the first lesson about DMVPN we discussed the basics of multipoint GRE and NHRP. The second lesson was a basic configuration of DMVPN phase 1. This time i'll explain how you can configure DMVPN phase 2. Once we have a basic configuration then we can try to run RIP, EIGRP, OSPF and BGP on top of i



Let’s start with the hub configuration:

Hub(config)#interface Tunnel0
Hub(config-if)#ip address 172.16.123.1 255.255.255.0
Hub(config-if)#ip nhrp authentication DMVPN
Hub(config-if)#ip nhrp map multicast dynamic
Hub(config-if)#ip nhrp network-id 1
Hub(config-if)#tunnel source GigabitEthernet0/1
Hub(config-if)#tunnel mode gre multipoint
Hub(config-if)#end

The configuration of the hub above is exactly the same as in DMVPN phase 1, no changes here. Let’s look at the spoke routers:

Spoke1(config)#interface Tunnel0
Spoke1(config-if)#ip address 172.16.123.2 255.255.255.0
Spoke1(config-if)#ip nhrp authentication DMVPN
Spoke1(config-if)#ip nhrp map 172.16.123.1 192.168.123.1
Spoke1(config-if)#ip nhrp map multicast 192.168.123.1
Spoke1(config-if)#ip nhrp network-id 1
Spoke1(config-if)#ip nhrp nhs 172.16.123.1
Spoke1(config-if)#tunnel source GigabitEthernet0/1
Spoke1(config-if)#tunnel mode gre multipoint
Spoke2(config)#interface Tunnel0
Spoke2(config-if)#ip address 172.16.123.3 255.255.255.0
Spoke2(config-if)#ip nhrp authentication DMVPN
Spoke2(config-if)#ip nhrp map 172.16.123.1 192.168.123.1
Spoke2(config-if)#ip nhrp map multicast 192.168.123.1
Spoke2(config-if)#ip nhrp network-id 1
Spoke2(config-if)#ip nhrp nhs 172.16.123.1
Spoke2(config-if)#tunnel source GigabitEthernet0/1
Spoke2(config-if)#tunnel mode gre multipoint

The configuration above is exactly the same as in DMVPN phase 1 except for two commands:

  • We removed the tunnel destination command.
  • We added the tunnel mode command to use GRE multipoint.

That’s it! We now have a DMVPN phase 2 network. Let’s verify our work…

Verification

First we should check if the hub has received some NHRP registrations from the spoke routers:

Hub#show dmvpn 
Legend: Attrb --> S - Static, D - Dynamic, I - Incomplete
        N - NATed, L - Local, X - No Socket
        T1 - Route Installed, T2 - Nexthop-override
        C - CTS Capable
        # Ent --> Number of NHRP entries with same NBMA peer
        NHS Status: E --> Expecting Replies, R --> Responding, W --> Waiting
        UpDn Time --> Up or Down Time for a Tunnel
==========================================================================

Interface: Tunnel0, IPv4 NHRP Details 
Type:Hub, NHRP Peers:2, 

 # Ent  Peer NBMA Addr Peer Tunnel Add State  UpDn Tm Attrb
 ----- --------------- --------------- ----- -------- -----
     1 192.168.123.2      172.16.123.2    UP 00:09:48     D
     1 192.168.123.3      172.16.123.3    UP 00:09:56     D

Above we see two registrations with the NBMA and tunnel addresses of our spoke routers. Let’s use the same command on the spoke routers:

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