DMVPN with IPsec Phase 3

Introduction

This article contains instructions on how to configure DMVPN Phase 3 between a "Hub" and two "Spokes" using Teltonika devices.

### Some description about what is DMVPN and benefits of phase 3 would be nice to have here. Probably don't need much, but a summary about what it is should be here.

### Most notably how phase 3 is beneficial - would be great to have a comparison of phase 2 vs phase 3

Prerequisites and overview

You will need:

• 2 Teltonika Routers for "Spokes" and one for "Hub"
• A PC to configure the routers
• HUB must have a Public IP address

### Recommended to segment spokes and hub requirements here. At a minimum we will need 2 spokes to demonstrate this issue, and as a separate requirement, at least 1 hub with a public IP address.

HUB configuration

This section contains information on how to configure DMVPN HUB. Firstly, we'll configure the DMVPN instance to make the connection possible. Then we'll set the Border Gateway Protocol (BGP) parameters as our dynamic routing solution.

Note: at the moment, BGP is the only stable dynamic routing solution that can work with DMVPN.

HUB configuration: DMVPN

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Navigate to the Services → VPN → DMVPN page and follow the instructions provided below.

Step 1: create a new DMVPN instance:

- Select your HUB interface in the Tunnel source field

- Set Local GRE interface IP address (for example, 10.0.0.254)

### GRE netmask should be an entire subnet, /24 or however many spokes we expect to connect to this hub

### We can still use 10.0.0.254, but with a netmask of 255.255.255.0 for example

- Set GRE MTU value to 1476

### One note - if we use mobile, I recommend using lower MTU value, maybe 1420 or even lower, down to 1400 or so. I think using 1420 in this example would be better

### There have been situations when mobile MTU is not consistent, depending on carrier, which would break connections when packets had to be fragmented

### Outbound/inbound keys are optional, but worth to mention why they are here and what they are for

- Set IPsec Pre-shared key (we used simple 123456 for this example)

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Step 2: configure DMVPN Phase 1 parameters:

- Encryption algorithm - AES 128

- Authentication SHA1

- DH group - MODP1024

### I don't recommend these parameters, they are not secure. Anything at or below the following shouldn't be used:

### AES-128

### Auth SHA256

### DH group - MODP3072 or ECP256

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Step 3: configure DMVPN Phase 2 parameters:

- Encryption algorithm - 3DES

- Hash algorithm - MD5

- PFS group -MODP768

### Same story here, try to increase security level here to a more secure solution.

### IPsec Phase 2 settings generally uses slightly lower parameters, because those algorithms are responsible for encrypting actual data traffic that we want to send over the IPsec tunnel

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Step 4: configure DMVPN NHRP parameters:

### Highlight the importance of "Redirect option here". This is essentially what makes P3 possible.

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Step 5: save changes

Hub configuration: BGP

Navigate to the Network → Routing → Dynamic Routes → BGP Protocol page and follow the instructions provided below.

Step 1: enable BGP and configure General section:

- Enable vty

- Set AS to 65000

- Set announcement network(s). Routes to these networks will be shared over BGP. We used 192.168.1.0/24

### Highlight the fact that "NHRP routes" selection should exist under "Redistribution options"

### Probably a good idea to set BGP router ID here using GRE interface IPs to avoid confusion and make troubleshooting easier

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Step 2: Create BGP Peer Group:

- Add Neighbor address (We used 10.0.0.1 and 10.0.0.2)

### Explanation needed what these IP addresses are - this might not be clear enough for end-users that this is spoke devices GRE IP address

### Also need to quickly mention about other settings

### Remote AS is empty here - I don't remember now, but is this intended?

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Step 3: Add two BGP peers for each spoke:

### Need to mention that "Let's move on to spokes BGP configuration now.", because it looks a bit confusing

Peer 1.

- Set Remote AS to 65001

- Set Remote address as 10.0.0.1

Peer 2.

- Set Remote AS to 65002

- Set Remote address as 10.0.0.2

### Briefly mention that other fields are not mandatory, but changes can be done if needed (aka "we will keep other settings as their default values for this configuration example" statement)

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Spoke 1 configuration: DMVPN

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### I think this should be done before dynamic routing configuration on each spoke, just to have IPsec tunnel and GRE IPs set for us

Navigate to the Services → VPN → DMVPN page and follow the instructions provided below.

Step 1: create a new DMVPN instance:

### I recommend to explain each step here in detail, for example:

- Add HUB address ### - this is the public IP address of previously configured hub device

- Select Tunnel source ### - this is the egress interface, which will be able to reach hub device's public IP address over the internet

- Add Local GRE interface IP address ### - this is the GRE IP address of "Spoke 1". It should be unique in the entire VPN network

- Add Remote GRE interface IP address ### - this is the GRE IP address of the previously configured hub device

- Set GRE MTU ### - this value should be set to the same value that was configured on the hub device. In our case, it is "1400"

- Set Local identifier, Remote identifier as %any and input same Pre-shared key ### brief explanation why this is needed would be nice as well

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Step 2: configure DMVPN Phase 1 parameters:

- Select Encryption algorithm - AES 128

- Select Authentication SHA1

- Select DH group MODP1024

### Same comment from hub section applies, increase security level

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Step 3: configure DMVPN Phase 2 parameters:

- Select Encryption algorithm 3DES

- Select Hash algorithm MD5

- Select PFS group MODP768

### Same comment from hub section applies, increase security level

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Step 4: configure DMVPN NHRP parameters:

- Leave everything by default

### Once again, highlight importance of "Redirect" option here

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Step 5: save changes

Spoke 1 configuration: BGP

Navigate to the Network → Routing → Dynamic Routes → BGP Protocol page and follow the instructions provided below.

Step 1: enable BGP and configure General section:

- Enable vty

- Set AS to 65001

- Set Network to 192.168.10.0/24

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Step 2: Create BGP Peer:

- Set Remote AS to 65000

- Set Remote address to 10.0.0.254

Spoke 2 configuration: DMVPN

### Same points and comments apply here just as it was in Spoke 1 config section

Navigate to the Services → VPN → DMVPN page and follow the instructions provided below.

Step 1: create a new DMVPN instance:

- Input your HUB address

- Select Tunnel source interface

- Set Local GRE interface address to 10.0.0.2

- Set Remote GRE interface IP address to 10.0.0.254

- Set GRE MTU to 1476

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Step 2: configure DMVPN Phase 1 parameters:

- Select Encryption algorithm - AES 128

- Select Authentication SHA1

- Select DH group MODP1024

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Step 3: configure DMVPN Phase 2 parameters:

- Select Encryption algorithm 3DES

- Select Hash algorithm MD5

- Select PFS group MODP768

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Step 4: configure DMVPN NHRP parameters:

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Step 5: save changes

Spoke 2 configuration: BGP

Navigate to the Network → Routing → Dynamic Routes → BGP Protocol page and follow the instructions provided below.

Step 1: enable BGP and configure General section:

- Enable vty

- Set AS to 65002

- Set Network to 192.168.20.0/24

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Step 2: Create BGP Peer:

- Set Remote AS to 65000

- Set Remote address to 10.0.0.254

Important Note

### Explanation why this is needed is recommended, because naturally a question comes to mind "why" this is needed

For HUB in Network > Firewall GRE zone change from REJECT to ACCEPT on FORWARD.

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For setups behind NAT specify Local identifier in the Services → VPN → DMVPN → IPsec section

### Didn't we already set this during spoke configuration? It's a good point to mention/explain, but I don't think this should be at the bottom of the article, but instead should be next to IPsec config of each spoke

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### Need to show working configuration with pings or something. Also to verify that Phase 3 DMVPN condition is actually working.