Lesson Contents
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:
Above we have two spoke routers and one hub, our underlay network uses 192.168.123.0/24 and the overlay network uses 172.16.123.0/24. Each router has a loopback interface with a network that we can advertise in RIP.
Configuration
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 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
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 destination 192.168.123.1
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 destination 192.168.123.1
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.
1 192.168.123.2 172.16.123.2 UP 00:22:37 D
1 192.168.123.3 172.16.123.3 UP 00:00:32 D
And we want to make sure that we can ping all tunnel IP addresses:
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 = 6/6/8 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 = 5/6/9 ms
Now we can focus on the RIP configuration…
RIP
Let’s enable RIP on all routers:
Hub(config)#router rip
Hub(config-router)#version 2
Hub(config-router)#network 1.0.0.0
Hub(config-router)#network 172.16.0.0
Hub(config-router)#no auto-summary
Spoke1(config)#router rip
Spoke1(config-router)#version 2
Spoke1(config-router)#network 2.0.0.0
Spoke1(config-router)#network 172.16.0.0
Spoke1(config-router)#no auto-summary
Spoke2(config)#router rip
Spoke2(config-router)#version 2
Spoke2(config-router)#network 3.0.0.0
Spoke2(config-router)#network 172.16.0.0
Spoke2(config-router)#no auto-summary
Now let’s see what we have…
Hub#show ip route rip
2.0.0.0/32 is subnetted, 1 subnets
R 2.2.2.2 [120/1] via 172.16.123.2, 00:00:07, Tunnel0
3.0.0.0/32 is subnetted, 1 subnets
R 3.3.3.3 [120/1] via 172.16.123.3, 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
----- --------------- --------------- ----- -------- -----
1 192.168.123.2 172.16.123.2 UP 00:29:29 D
1 192.168.123.3 172.16.123.3 UP 00:07:24 D
When we want to reach 2.2.2.2/2 we will use 172.16.123.2 as the next hop. In our NHRP cache we see that we need to use NBMA address 192.168.123.2 to get there.
What about the spoke routers, did they learn anything?
Spoke1#show ip route rip
1.0.0.0/32 is subnetted, 1 subnets
R 1.1.1.1 [120/1] via 172.16.123.1, 00:00:17, Tunnel0
Spoke2#show ip route rip
1.0.0.0/32 is subnetted, 1 subnets
R 1.1.1.1 [120/1] via 172.16.123.1, 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?
I found the definition below of NMBA :
In the article :
https://networklessons.com/cisco/ccnp-route/ospf-non-broadcast-network-type-over-frame-relay/
According to that ; it seems that NBMA is that “kind-of Frame-Relay network” DMVPN builds on the underlay Network.
I realised at least on my lab that using the command “ip summary address rip 0.0.0.0 0.0.0.0” 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.
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 thedefault-information originate
command.These two commands do different things.
... Continue reading in our forumDefault-information originate
will advertise default route, whileip summary-address rip 0.0.0.0 0.0.0.0
will advertise only default route and will hide topology details. Remember that theip summary-address
command can use a more specific route, such asip summary-address rip 10.2.0.0 255.255.0.0
, it does not have to be 0.0.0Hello 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.
regards,
Tariq
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