Re: Eero devices expose LAN to SP during reboot

[Brandon Martin via NANOG <nanog () lists nanog org>]

On 9/16/26 17:16, Tom Smyth wrote:
> hi Brandon... it sounds like alan-bypass is enabled ( usually by jumpers 
> or a dip switch on the router
>
> it is an 8 pole relay between two nic interfaces for passing through 
> traffic in the event of a failure of a router... ( config for appropiate 
> use of bypass is p1 uplink connected to a primary router with a 
> lanbypass as a group or( when the device is booted up acts as a layer 2 
> bridge )  then the backup router is plugged into the second port of tje 
> lanbypass group
>
> so the router acts like a layer 1 passthrough cable to the 2nd router 
> when it is switched off or being reset
> ( and in normal operation a layer2 device exposing the bridged wan of 
> the primary router and the wan of 2ndary router to the 1 port of yhe 
> upstream ntu...
I didn't even know they had this feature.  My google-fu (and 
duckduckgo-fu) also fails to find any references to it, but Eero's 
documentation is sort of scattered.

The Eero was bought through retail channels.  Would they ship it with 
this feature enabled?  I wouldn't think so.  It's plausible it was a 
re-packaged return.

I don't think their Eero is configured in bridge mode.  They certainly 
wouldn't have set it to that intentionally, and Eero hides that setting 
pretty well.

Everything seems to work properly once the Eero finishes rebooting.  It 
takes over routing and NAT functions and reliably exposes just one MAC 
to the SP network after that point.

Note if you're unfamiliar with the Eero: It's a very consumer-oriented 
device with software to match.  The device has two unidentified ports, 
and all configuration happens through a mobile app.  It uses largely 
undocumented heuristics to figure out what to do for each given use 
case.  It usually seems to get it right, but in this case, it's doing 
something very bad.

I have other customers using Eeros with no apparent problems, so it's 
possible that this customer fat-fingered a setting somewhere.
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