DMVPN Phase 1 RIP Routing

In the first DMVPN lesson I explained some of its basics, in the second lesson I explained how to create a basic DMVPN phase 1 configuration. In this lesson, we’ll take a look how RIP behaves on DMVPN phase 1.

Here’s the topology we will use:

DMVPN Example Topology loopbacks

Above we have two spoke routers and one hub, our underlay network uses and the overlay network uses Each router has a loopback interface with a network that we can advertise in RIP.


Tunnel Interfaces

Here is the configuration of the tunnel interfaces on the hub and spoke routers. I explained these commands in the DMVPN phase 1 basic configuration lesson so I’m not going to discuss them again:

Hub(config)#interface Tunnel0
Hub(config-if)#ip address
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
Spoke1(config)#interface Tunnel0
Spoke1(config-if)#ip address
Spoke1(config-if)#ip nhrp authentication DMVPN
Spoke1(config-if)#ip nhrp map
Spoke1(config-if)#ip nhrp map multicast
Spoke1(config-if)#ip nhrp network-id 1
Spoke1(config-if)#ip nhrp nhs
Spoke1(config-if)#tunnel source GigabitEthernet0/1
Spoke1(config-if)#tunnel destination
Spoke2(config)#interface Tunnel0
Spoke2(config-if)#ip address
Spoke2(config-if)#ip nhrp authentication DMVPN
Spoke2(config-if)#ip nhrp map
Spoke2(config-if)#ip nhrp map multicast
Spoke2(config-if)#ip nhrp network-id 1
Spoke2(config-if)#ip nhrp nhs
Spoke2(config-if)#tunnel source GigabitEthernet0/1
Spoke2(config-if)#tunnel destination

Let’s do two quick checks, we want to make sure that both spokes are registered to the hub:

Hub#show dmvpn | begin 192.168.123.
     1    UP 00:22:37     D
     1    UP 00:00:32     D

And we want to make sure that we can ping all tunnel IP addresses:

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 6/6/8 ms
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 5/6/9 ms

Now we can focus on the RIP configuration…


Let’s enable RIP on all routers:

Hub(config)#router rip
Hub(config-router)#version 2
Hub(config-router)#no auto-summary
Spoke1(config)#router rip
Spoke1(config-router)#version 2
Spoke1(config-router)#no auto-summary
Spoke2(config)#router rip
Spoke2(config-router)#version 2
Spoke2(config-router)#no auto-summary 

Now let’s see what we have…

Hub#show ip route rip is subnetted, 1 subnets
R [120/1] via, 00:00:07, Tunnel0 is subnetted, 1 subnets
R [120/1] via, 00:00:06, Tunnel0

Our hub router has learned both networks on the loopback interfaces. Take a good look at the next hop IP addresses that we have here, these are the tunnel addresses. When the hub wants to reach these networks, it will have to check NHRP to find the NBMA addresses:

Hub#show dmvpn | begin Hub
Type:Hub, NHRP Peers:2, 

 # Ent  Peer NBMA Addr Peer Tunnel Add State  UpDn Tm Attrb
 ----- --------------- --------------- ----- -------- -----
     1    UP 00:29:29     D
     1    UP 00:07:24     D

When we want to reach we will use as the next hop. In our NHRP cache we see that we need to use NBMA address to get there.

What about the spoke routers, did they learn anything?

Spoke1#show ip route rip is subnetted, 1 subnets
R [120/1] via, 00:00:17, Tunnel0
Spoke2#show ip route rip is subnetted, 1 subnets
R [120/1] via, 00:00:08, Tunnel0

Our spoke routers only have one entry, the network on the loopback interface of the hub router. What went wrong here?

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Forum Replies

  1. I realised at least on my lab that using the command “ip summary address rip” does not inject a default route on the spokes, you also have to include the command “default-information originate” under the “router rip” for this to take effect.

  2. Hello Tariq

    It seems that others are having similar issues with the ip summary address command when using the RIP protocol. Even so, the solution is not the default-information originate command.

    These two commands do different things.

    Default-information originate will advertise default route, while ip summary-address rip will advertise only default route and will hide topology details. Remember that the ip summary-address command can use a more specific route, such as ip summary-address rip, it does not have to be 0.0.0

    ... Continue reading in our forum

  3. Hello Laz,

    Thank you for the feedback, however I decided to simulate again with a vIOS and I received the summary-address as expected, so I guess the issue might be a bug on the initial IOS I was using which was the IOS 15.2 on a 7200.



  4. Hi Laz,

    I am having doubt about TTL, as per 1,2,3 packet I am getting TTL= 255 at spoke 1 when it will send packet to hub TTL received by hub must be 254 and it will forward packet by changing TTL to 253 which will be received by spoke 2 and same in case of when spoke 2 tries to communicate to spoke 1 and in response TTL send by both spokes must be 253 not 255, Kindly suggest still confused in it .

    Secondly I am unable to understand split horizon here, b/w two directly connected interface interface i can understand but here single tunnel at Hub connected to t

    ... Continue reading in our forum

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