MicroNugget: How to Verify DMVPNs

In this video, Keith Barker covers verifying the implementation of a DMVPN. If you're using a dynamic multipoint VPN, the four necessary ingredients — mGRE, NHRP, IGP and IPsec — all need to be configured and confirmed for the network to operate properly.

In a DMVPN, one device with a static IP address acts as a hub for the network. Like all devices connected to the DMVPN, it'll have a multipoint GRE (mGRE) interface, but the spokes of the network can have dynamic IP addresses, so long as they're reachable. When the spokes come online, they register with the hub device — that creates a logical path between each spoke and the hub. IPsec then secures those paths.

IGP is used to advertise the spoke networks up to the hub, and then down to each of the other spokes. Then, when a spoke network needs to connect to a different network, it discovers it in its mGRE interface, and uses the Next Hop Resolution Protocol (NHRP) to find the right address. Up to that point, those spoke networks didn't know each other's IP addresses, but a tunnel gets created between them and protected by IPsec. Keith films himself navigating the steps for configuring and verifying the DMVPN so you don't miss a single step.

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[arsimzeka]

I enjoy every Video from Keith Barker 

[skazemisk]

Hi Keith,

I tried to setup EIGRP over DMVPN in GNS3.
DMVPN working properly, (I verffied based on your nugget) and EIGRP neighbors are formed, but after a while I received following error:

%DUAL-5-NBRCHANGE: IP-EIGRP(0) 110: Neighbor 172.16.0.2 (Tunnel0) is down: retry limit exceeded

more info:
- GNS 3
- IOS 12.4
- used Serial link to middle router and static route to reach branch.
- Tunnel formed properly
- Multicast is mapped to physical IP address of the hub.

Do you have any idea?

Regards
S.K