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:

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

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:

Spoke1#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:Spoke, NHRP Peers:1,

# Ent Peer NBMA Addr Peer Tunnel Add State UpDn Tm Attrb
----- --------------- --------------- ----- -------- -----
1 192.168.123.1 172.16.123.1 UP 00:04:51 S

Spoke2#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:Spoke, NHRP Peers:1, 

 # Ent  Peer NBMA Addr Peer Tunnel Add State  UpDn Tm Attrb
 ----- --------------- --------------- ----- -------- -----
     1 192.168.123.1      172.16.123.1    UP 00:04:35     S

Above we can see that both spoke routers have an entry for the hub. Let’s see if we can ping the spoke routers from the hub:

Hub#ping 172.16.123.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.123.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 5/7/11 ms

Hub#ping 172.16.123.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.123.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 6/7/10 ms

Excellent this seems to be working! We can now use this basic configuration to play with some routing protocols.

hostname Hub
!
interface Loopback0
 ip address 1.1.1.1 255.255.255.255
!
interface Tunnel0
 ip address 172.16.123.1 255.255.255.0
 no ip redirects
 ip nhrp authentication DMVPN
 ip nhrp map multicast dynamic
 ip nhrp network-id 1
 tunnel source GigabitEthernet0/1
 tunnel mode gre multipoint
!
interface GigabitEthernet0/1
 ip address 192.168.123.1 255.255.255.0
 duplex auto
 speed auto
 media-type rj45
!
end

hostname Spoke1
!
interface Loopback0
 ip address 2.2.2.2 255.255.255.255
!
interface Tunnel0
 ip address 172.16.123.2 255.255.255.0
 no ip redirects
 ip nhrp authentication DMVPN
 ip nhrp map 172.16.123.1 192.168.123.1
 ip nhrp map multicast 192.168.123.1
 ip nhrp network-id 1
 ip nhrp nhs 172.16.123.1
 tunnel source GigabitEthernet0/1
 tunnel mode gre multipoint
!
interface GigabitEthernet0/1
 ip address 192.168.123.2 255.255.255.0
 duplex auto
 speed auto
 media-type rj45
!
end

hostname Spoke2
!
interface Loopback0
 ip address 3.3.3.3 255.255.255.255
!
interface Tunnel0
 ip address 172.16.123.3 255.255.255.0
 no ip redirects
 ip nhrp authentication DMVPN
 ip nhrp map 172.16.123.1 192.168.123.1
 ip nhrp map multicast 192.168.123.1
 ip nhrp network-id 1
 ip nhrp nhs 172.16.123.1
 tunnel source GigabitEthernet0/1
 tunnel mode gre multipoint
!
interface GigabitEthernet0/1
 ip address 192.168.123.3 255.255.255.0
 duplex auto
 speed auto
 media-type rj45
!
end

Conclusion

Changing your DMVPN phase 1 configuration to phase 2 is pretty straight forward. You remove the static tunnel destinaton on the spoke routers and we turn the GRE interfaces into GRE multipoint, that’s it.

The challenge will be to configure routing protocols on top of it which we will do in the following lessons:

• DMVPN Phase 2 RIP Routing
• DMVPN Phase 2 EIGRP Routing
• DMVPN Phase 2 OSPF Routing
• DMVPN Phase 2 BGP Routing

If you have any questions, feel free to leave a comment!