Private relay service is a new VPN-like service from Apple that is included in Icloud Plus subscriptions. It’s still in beta but is included in the regular version of Mac OS Monterey.
When you activate the function, it starts sending data over the quic protocol to servers at Apple, and nothing seems to be able to stop it, writes the Swedish vpn service Mole in a blog post.
If you stop all traffic on port 443 over udp (which quic uses) with Mac OS’s built-in firewall, the system should not be able to contact Apple’s servers, but the traffic will continue. The same applies if you connect to a VPN service and set up your computer to send all Internet traffic over it.
In the latter case, it is not only that the traffic is let through – it is not sent at all over the VP but directly, with the computer’s own IP address.
Because the traffic to Apple is encrypted, Mullvad cannot know what is being sent, nor whether it is actually part of a private relay service or whether it is only activated when that function is switched on. Mole speculates that it is just a kind of “ping” to tell the servers that the computer is still active, but as I said, it can not be determined.
If you turn off private relay service, the traffic disappears completely, and firewall rules and VPN connections work fully.