DMVPN Phase 1 EIGRP Routing

In the first DMVPN lesson we discussed the basics and the three different phases. I also showed you how to create a basic DMVPN phase 1 configuration. In this lesson we’ll use that basic configuration and configure EIGRP on top of it. Here’s the topology we will use:

Each router has a loopback interface with an IP address that we’ll advertise in EIGRP.

Configuration

Tunnel interfaces

Here is the tunnel configuration of the hub and spoke routers:

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 some quick checks to verify that the tunnels are working correctly:

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

We see two NHRP registrations on the hub, let’s do a quick ping:

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

No issues here…let’s configure EIGRP.

EIGRP

Let’s advertise all networks:

Hub(config)#router eigrp 123
Hub(config-router)#network 1.1.1.1 0.0.0.0
Hub(config-router)#network 172.16.123.0 0.0.0.255
Hub(config-router)#no auto-summary 

Spoke1(config)#router eigrp 123
Spoke1(config-router)#network 172.16.123.0 0.0.0.255 
Spoke1(config-router)#network 2.2.2.2 0.0.0.0
Spoke1(config-router)#no auto-summary

Spoke2(config)#router eigrp 123
Spoke2(config-router)#network 172.16.123.0 0.0.0.255
Spoke2(config-router)#network 3.3.3.3 0.0.0.0
Spoke2(config-router)#no auto-summary 

Let’s make sure we see two neighbors on the hub:

Hub#show ip eigrp neighbors 
EIGRP-IPv4 Neighbors for AS(123)
H   Address                 Interface              Hold Uptime   SRTT   RTO  Q  Seq
                                                   (sec)         (ms)       Cnt Num
1   172.16.123.3            Tu0                      11 00:00:31   13  1434  0  4
0   172.16.123.2            Tu0                      13 00:01:02   82  1434  0  4

So far so good, let’s check our routing tables:

Hub#show ip route eigrp 

      2.0.0.0/32 is subnetted, 1 subnets
D        2.2.2.2 [90/27008000] via 172.16.123.2, 00:01:16, Tunnel0
      3.0.0.0/32 is subnetted, 1 subnets
D        3.3.3.3 [90/27008000] via 172.16.123.3, 00:00:48, Tunnel0

The hub router has two entries, the next hop IP addresses are the tunnel addresses of spoke 1 and 2. When we want to resolve them, we’ll have to check the information in the NHRP cache:

Hub#show dmvpn | begin Hub
Type:Hub, NHRP Peers:2, </code>

# Ent Peer NBMA Addr Peer Tunnel Add State UpDn Tm Attrb
----- --------------- --------------- ----- -------- -----
1 192.168.123.2 172.16.123.2 UP 00:30:11 D
1 192.168.123.3 172.16.123.3 UP 00:21:28 D

This is how the hub is able to reach both spoke routers. What about the spoke routers?

Spoke1#show ip route eigrp 

      1.0.0.0/32 is subnetted, 1 subnets
D        1.1.1.1 [90/27008000] via 172.16.123.1, 00:01:27, Tunnel0

Spoke2#show ip route eigrp 

      1.0.0.0/32 is subnetted, 1 subnets
D        1.1.1.1 [90/27008000] via 172.16.123.1, 00:01:01, Tunnel0

Like RIP, EIGRP is a distance vector routing protocol so we have split horizon issues. The spoke routers don’t see each other’s networks. Let’s fix this for now: