MX-64 and MG-52

[Chema-Spain]

Hi,

Customer previously had an SDWAN network comprising MX64 at branches. I know this MX model is quite old. Their topology was a FTTH in wan1 and a 4G USB Dongle as BU. We replaced those BUs with external Meraki MG-52 in bridge mode. Customer is complaining MX blackholes traffic when ftth fails (packet loss periods, interface up). According to him, it did not happen with Dongle BU's in place. It doesn't make sense to me as I think convergence time should be the same. At the end of the day, convergence time is based on same probes... however, customer insists in the opinion it only happens after changing BU topology. Network size is around 140 branches and they ensure they have seen this issue in ramdomly in many of them. Can you find an explanation that could cause this behaviour? Thanks!

[alemabrahao]

When connected directly to the MX, the dongle was managed by the MX. If the FTTH link failed, the MX could immediately switch to the cellular interface because it had full control over both WAN interfaces.

The MG-52 presents the cellular link as an Ethernet interface. If FTTH fails but the physical link remains up (e.g., ONT still powered, no carrier loss), the MX still sees WAN1 as “up” at Layer 1/2.

MX64 is EOL, newer MX models handle these scenarios better.

[Chema-Spain]

Thanks for your quick response.

I don't catch you well: In case FTTH fails, in order to detect such an indirect failure, MX has the same probe both having a usb dongle or an external MG. It should follow same failure detection mecanishm regardless of the current BU topology.  https://documentation.meraki.com/SASE_and_SD-WAN/MX/Design_and_Configure/Configuration_Guides/Firewa...

SIMs are not the same, we replaced them when installing MG52, different provider. However, as MX has dashboard access also from uplink wan2 connected to the MG  (status ready for wan2) I can't blame it to the SIM behaviour.

Thanks!