I'm sharing an excellent document where you can find beside of the best practices configuring DMVPN, some of the most common problems we usually face when deploying this technology and how to approach a troubleshooting step by step.
Please take a look at this document and do not hesitate if you have further questions.
We have various service provider connections--some are better than others. Across the Cellular connections an MTU of 922 is often the best we can achieve, while on quality Fiber connections we can achieve the tunnel max of MTU 1476.
My question is related to performance: should we establish multiple DMVPN endpoints? One for the "better" connections and one for the rest?
When planning to deploy DMVP you have to follow some best practices to avoid any issues. One of the the best practices recommended on Cisco Design and impementation guide :
IP MTU – Set the IP maximum transmission unit (MTU) to 1400 on all DMVPN tunnel interfaces to eliminate the potential for fragmentation. GRE and IPsec headers add about 60 bytes to the packet, and cause the router to fragment larger packets if this exceeds the interface MTU, straining the CPU.
TCP MSS – Set the TCP maximum segment size (MSS) value to 1360 on all DMVPN tunnel interfaces. This value is calculated by subtracting 40 bytes from the IP MTU value. Use the command ip tcp adjust-mss 1360 to set the value on the mGRE tunnel interface toward the spokes. This helps TCP sessions adjust to the lower MTU and is needed if Path MTU Discovery (PMTUD) does not work between end hosts.
Concerning the question about performance, It always depends on what kind of traffic is the most important on your environment, what Apps you need to keep up and running, based on that information you can think about what is the best design for your network .
What are the best practices for a multi-hub DMVPN phase 3 environment?
Are there any configuration considerations for the tunnels that is different than a single hub?
Also, how would you configure EIGRP on the hubs/spokes in regards to summaries & split horizon in this scenario?
Take a look at the following link. you will find an excellent document about Design and implementation of DMVPN.
Thanks for sharing your knowledge and for all the great assistance you’ve provided here. We kindly appreciate it, you’re an important contributor of this community