[ninkendo]

I guess different captive portals work differently, because I’ve heard of plenty of them that can be bypassed by simply statically assigning the address of someone else who’s already authenticated (ie session hijacking), but it makes sense that any “decent” captive portal system uses MAC addresses to mitigate this.

The randomization I refer to is of the outgoing IPv6 address, not the MAC address… nothing that I’m aware of randomly cycles MAC addresses (Apple’s OSes can be configured to randomly generate a MAC every time you connect to a network, but it won’t regenerate them continuously in a session. IPv6 addresses however are continuously generated, as per the RFC4941 spec.) If the system is using MAC addresses to identify users, then temporary/cycled IPv6 addresses should be no problem.