It appears to automatically detect and bridge: https://support.eero.com/hc/en-us/articles/204144995-Can-I-still-use-eero-if-I-have-a-modem-with-a-built-in-route

It appears to automatically detect and bridge: https://support.eero.com/hc/en-us/articles/204144995-Can-I-still-use-eero-if-I-have-a-modem-with-a-built-in-router- https://support.eero.com/hc/en-us/articles/204144995-Can-I-s... > your modem's built-in router will continue to manage the network unless you can turn off the routing functionality. That means that eero won't manage your firewall, your NAT or your DHCP settings. I'd guess if it gets an RFC 1918 address from upstream it turns off NAT and DHCP.