Seems easy enough to require (i.e. regulate) end-customer ISPs to drop any traffic with a source IP that isn't assigned to the modem it's coming from. This woul

Seems easy enough to require (i.e. regulate) end-customer ISPs to drop any traffic with a source IP that isn't assigned to the modem it's coming from. This would at least prevent spoofing from e.g. compromised residential IoT devices. Are they not already doing that filtering? Is there any legitimate use-case to allow that kind of traffic?