Known protocols for supporting mobility in relation to Internet Protocol (IP) networks are not able to efficiently support distribution of Binding Update messages to Correspondent Nodes (104) in a set of fixed IP networks (102). Consequently, the present invention makes use of a multi-cast service provided by the IPv6 protocol in order to deliver Binding Update messages to the Correspondent Nodes (104). The use of the multi-cast service to deliver Binding Update messages avoids a proliferation of such messages which would occur under know protocols requiring a mobile node (106,107) to send the Binding Update message to each Correspondent Node (104). Consequently, use of bandwith in the set of fixed IP networks (102) is more efficient.