MX not failing over to cellular (USB)

[IvoBiermans]

Hi All,

Have quite a few locations that have an MX with a VDSL connection as its main internet. Due to it being a VDSL connection we have had to use the providers modem/router to facilitate the connection. Unfortunately the providers modem is not capable of being set into bridge mode (Arg.. 😞 ) So in effect the Meraki is running in double NAT.

We also have a 4G backup USB modem plugged into it as fail-over.

The issue we have is that if there is an upstream failure (soft failure) on the primary connection (VDSL) the Meraki does not seem to failover to the Cellular.

Reading the documentation on failover it mentions it will only failover if all 3 test fail (internet, DNS, and ARP). But in my case ARP will never fail because the providers router is still on, albeit with no working uplink.

https://documentation.meraki.com/MX/Firewall_and_Traffic_Shaping/Connection_Monitoring_for_WAN_Failo...

Apart from trying to obtain VDSL modems that are capable of bridging does anyone else have any experience on what can be done?

[PhilipDAth]

First it does a DNS test.  If that fails - the link is marked as down.

If DNS is up then it does the Internet test.  If all tests fail then the link is marked as down.  This will cover your case.

If all tests above pass then ARP is tested.  If that fails the link is marked as down.

The failover could take up to 5 minutes if you are waiting for the the Internet tests to fail before it brings up the cellular link.

[IvoBiermans]

Thanks for your reply @PhilipDAth 

Looking at the document it clearly indicates that all 3 test have to fail.

But as the router infront of the MX will still reply to ARP even if the upstream is down it will not mark it as failed...

Even Meraki support is confirming this. However this seems very strange to me and does not make much sense.

In my case Internet and DNS will fail but ARP would not.

Had 2 cases now where the Meraki did not failover, after 2 hours we had to call someone onsite to unplug the providers modem to simulate a hard failure on the WAN port.

[cmr · Accepted solution]

@IvoBiermans I think that if you have the 4G on WAN2 (as opposed to a USB modem) then what @PhilipDAth said applies and will solve your issue.   Ideally use an MG21 or similar, but any 4G router should work in this case.  You might get higher utilisation on the link though is the MX will perform more frequent tests on it.

[IvoBiermans]

@cmr Thank you for replying. I have come to the conclusion of this as well over the last couple of days. We will check what the best option will be. I find the MG21 too expensive for what it is, however just a simple 4G router with network uplink seems to be quite rare as well...

Anyway, thanks for the help to all who responded.