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HI,

I'm working on the DMVPN SIM using the GNS3 Lab and I am running into trouble here. I followed the configuration solutions, which is as follows:

BR1
interface tunnel 0
ip address 192.168.1.1 255.255.255.0
tunnel source e0/1
tunnel mode gre multipoint
tunnel key 100
ip nhrp network-id 100
ip nhrp authentication ccnp123
ip nhrp map 192.168.1.254 10.10.255.254
ip nhrp map multicast 10.10.255.254
ip nhrp holdtime 300
ip nhrp nhs 192.168.1.254

BR2
interface tunnel 0
ip address 192.168.1.2 255.255.255.0
tunnel source e0/1
tunnel mode gre multipoint
tunnel key 100
ip nhrp network-id 100
ip nhrp authentication ccnp123
ip nhrp map 192.168.1.254 10.10.255.254
ip nhrp map multicast 10.10.255.254
ip nhrp holdtime 300
ip nhrp nhs 192.168.1.254

with the crypto ipsec fragmentation before-encryption on both routers as well as ip mtu 1400 and ip tcp adjust-mss 1360. As well as applying the ipsec_profile. However, when I do the traceroute i get this:

tracing the route to 172.16.1.254
1 192.168.1.254 2 msec 1 msec 1msec
2 * * *
3* * *

%DMVPN-6-NHRP_RESOLUTION_REPLY: TUNNEL0: Host with (Tunnel: 192.168.1.1 NBMA: 10.10.255.1) Received Resolution Reply from (Tunnel: 172.16.2.254 NBMA: 10.10.255.254)

Some help or assistance to why the solution does not work would greatly be appreciated

Thanks 

The tunnel between the spokes BR1 and BR2 is dynamic and is only created when you ping or traceroute BR2 (172.16.2.254). Try tracerouting 2 to 3 times with some gap, and it'll eventually work. You should download the project file from the site again and try it.

(07-22-2025, 02:25 PM)help_desk Wrote: [ -> ]The tunnel between the spokes BR1 and BR2 is dynamic and is only created when you ping or traceroute BR2 (172.16.2.254). Try tracerouting 2 to 3 times with some gap, and it'll eventually work. You should download the project file from the site again and try it.

Yes, I tried this and it worked. However, i had to wait 3 mins and 20 seconds.