A method and arrangement are proposed for controlling access by a client node to multicast traffic via an access network. When a client node sends a message to an access node of the access network requesting access to a multicast channel, the access node modifies this request by adding identification information to the message for identifying the client node before forwarding it to a router capable of routing multicast traffic streams. The router uses the identification information to consult access data stored for the client node and returns an acknowledgement message to the access node, indicating whether access is permitted. If access is granted, the access node streams the multicast channel to the client node. Modifying the multicast request message using the access node to include identification information allows the access control to be performed in a more centralized manner while retaining the security of a port-based access control.