NightHawk MeshWiFi 6 system

[wildoaksman]

Can the Nighthawk mesh 6 system be connected to sierra wireless  Unite- 9859 WiFi Broadband or the Nighthawk M1?

[plemans]

The M1 has an ethernet port you can use to connect. But you need to make sure either the M1 is in passthrough mode or the Mesh system in AP (access point) mode to prevent a double nat. 

[wildoaksman]

How do I do that

[plemans]

Do what specifically? And for what device? 

You can go to netgear.com/support/   and type in the model number. it has manuals, guides, firmware, etc.