Abstract: Communication between a private network (1) and a roaming mobile terminal (4), the private network (1) including a home agent (5) for the mobile terminal and a gateway (2, 3) through which, the communication passes and which-provides security protection for the private network (1). The protocols of the communication include a security association between the mobile terminal (4) and the gateway (2, 3) for inbound communication and another security association for outbound communication. In response to a handover of communication causing an IP address. (MN Co @) of the mobile terminal (4), to change to a new IP address (MN: New Co @), the mobile terminal updates its inbound security association from the, gateway (2, 3) so that it can receive packets sent to it with the new IP address (MN New Co @) as destination.