Limit device traffic to only one MX uplink

Hi all

The Meraki MX devices gives you an easy way of automaticly use 2 uplinks. It works seamlessly but it’s hard to do some configuration that is possible on other Cisco devices.

One of those is to deny specific devices to connect over only 1 of the uplinks. Let’s say that WAN 1 is a fiber connection. You got enogh capacity to send and receive all kind of traffic. WAN 2 on the other hand is a sattelite connection. The 2 big drawbacks with sattelite is latency and speed. Sometimes even the cost per MB transferred. Often the guaranteed bandwith on a satelite connection could be as low as 64 kb/s. It’s not much bandwith for other devices then.

Then the big question is, how do you limit the connection to only use WAN 1. This could be a device that sync data every hour and would generate traffic or a whole subnet with guest wifi users. You don’t want these devices use your costly satelite connection. You do most likely need it for business critical applications.

I spent a few good hours trying to find a solution to this. I asked help from Meraki and various forums. I always got told that traffic shaping should help etc. But the only thing it does is giving me the preferred uplink, it never blocks the traffic from going online if the other WAN connection is down.

The solution I came up with was to turn off NAT when you use the interface that should be blocked. All the devices behind the Meraki that should be blocked does need to be in a seperate VLAN. In version 15 you can exclude specific VLAN from the NAT policy on the uplinks. The traffic will then stop since there is no return route for the traffic (as long as youo don’t add a static route).

So in the above example we want VLAN 20 to only have access over WAN 1 and not WAN 2. You start by finding the network you want to do the change on in the Meraki Dashboard. Then go to Security & SD-WAN and Adressing and VLAN’s on the left side. In the bottom of the page you have NAT exceptions where you can choose to disable NAT on the different uplinks. In my screenshot I have excepted Crew network from the NAT policy. With this config the devices on Crew VLAN can’t use WAN 2/Uplink 2.