Meraki MX /31

[Mosquitar]

Hi All,

I cant find an answer to this, but does anyone know if the Meraki MX supports /31 subnets on the WAN uplink interfaces?

Thanks

[PhilipDAth · Accepted solution]

It does not.

[Mosquitar]

That's a shame, I will need to use /30s instead.

Thanks for the response Philip

[WarrenG]

Has there been any progress on this in the last 5 years? We just got a new fiber connection installed for one of our clients, and they only provided a /31 static IP block. Any idea if this configuration is now supported?

[PhilipDAth]

A low comment says they were able to configure this, but did not test it.

[Owen]

The release notes for version 14.24 say it is possible. I have not tried it though.

[Mosquitar]

Hi Owen,

Ahh yes. I will try and test this when I can. Thank you.

• Added support for assigning a /31 subnet to the MX’s uplink via the local status page. The IP address assigned to the MX must be the higher of the two available IP addresses in the /31 subnet

[RobertoBertin]

Any luck with /31 mask test on the WAN interface of the MX?

[RobertoBertin]

I have tried to configure it in an inactive WAN interface through the dashboard (uplink tab) and it accepts it, but haven't yet tried on an active interface. We are using MX version 14.53.

[Tharp]

Really old post, just in case someone ends up here like I did. Just got a /31 WAN connection to work on an MX75 running 18.211.2

The trick for me was to set the subnet as a /24 255.255.255.0 with 8.8.8.8 DNS

Connected right up after that.

[jimmyt234]

/31 subnet mask should work on an MX running any kind of recent firmware, we have been using it for years.

[Tharp]

I would have thought so too but it couldn't find the Internet or Meraki Portal. Thinking maybe the fiber handoff was bad, I tried hooking a laptop to it. Windows definitely doesn't like a /31 and threw an error saving the IP information. Researching that, found others just entered a /24 instead. Laptop connected fine with supplied IP, Gateway, and 255.255.255.0.

After that, why not try the same on the MX. It connected no problem. Responded to open tickets with the ISP and Meraki on what fixed it. They agreed that was a valid workaround.

Just my experience.

[GIdenJoe]

On the pc you can temporarily fudge with the subnetmask but please on the MX do use the 255.255.255.254 mask to configure the uplink.  This works fine in recent releases.