A friend of mine has some trouble with his AirPort Extreme (Router). All of his clients (Macbook, iPad, iPhone, ...) do not connect to the internet, except one iMac in his office.
The AirPort Extreme is connected to a modem from his internet provider. If he connects a MacBook directly with the modem it has an internet connection.
I think all of the settings on the devices are the same as on the working iMac (IPv4 DHCP, IPv6 automatic).
Someone have an idea what I should check or a solution for this problem?