A switching node in a distributed transmission network. The node, which is assigned a unique switching node identity (SID) includes a number of switch ports for connection of a number of line boards with subscriber line ports. The node detects a request for an IP address from a line board and identifies the switch port on which the request is received. The node generates an extended IP address request message by adding information about the SID and the receiving switch port over which the IP address request was received. The node forwards the extended IP address request message to a control unit within the node or to an external switching control node.