A client and a host communicate in a packet data network including a plurality of routing nodes such as routers and firewalls. The host is configured to provide the client with a session and to detect the accessibility of the client by repeatedly sending keep-alive messages to the client. In order to reduce the traffic actually arriving at the client, at least some of the keep-alive message are adjusted such that their routing towards the client will be stopped before the client by storing in a Time-To-Live field specified in the Internet Protocol a value of maximum routing hops defined to correspond with the last routing node before the client on a route from the host to the client. The adaptation of the keep-alive message can also be configured to allow some keep-alive message to reach the client to occasionally test the communication path between the client and server.