The old DSL setup consisted of the sonic DSL/router/gateway device, with an airport extreme in bridge mode for better wifi performance. So, the sonic DSL/router/gateway device was doing NAT + DHCP for the network.
I didn't realize this initially, so I plugged the airport extreme directly into the new fiber ONT. Since it was in bridge mode, several devices in the apartment got direct public IP addresses from Sonic's infrastructure (no NAT, no local DHCP server in the apartment).
3 separate devices concurrently got public, routable IP addresses from Sonic, before I noticed and switched the Airport Extreme out of bridge mode (so it started doing NAT + DHCP internally).
What is Sonic's policy about this? Is it against the terms of service to have multiple devices connected directly to the ONT and receiving direct IP connectivity from Sonic? Will there at some point be technical limitations imposed on the number of concurrent DHCP leases?
My experience is with Cable systems, where a limit of 1 concurrent connected device is typically imposed by the ISP (i.e. only the first device will receive a DHCP lease; subsequent devices will not, unless you reboot the cable modem).