The UnkownHostException error can come for many reasons. To find out first there is a need to know the network's name SERVICE that is having a fully-qualified hostname RECOGNIZED by RMI host. The possible problems that might come are:

There is a POSSIBILITY of having misconfigured DHCP servers that allows fully-qualified domain name of RMI server machines. RMI client in this case try to access the outside server's DHCP domain that will make it unavailable for the server.

There is a possibility of having the error DUE to WINS server. It is possible that only registered users might not be reachable by hosts.

There is a possibility of having a firewall that is blocking the RMI client and server side requests. If the server resides inside the firewall and the client outside then the client won't be able to make any REMOTE calls to the server that is inside due to the firewall.

The UnkownHostException error can come for many reasons. To find out first there is a need to know the network's name service that is having a fully-qualified hostname recognized by RMI host. The possible problems that might come are:

There is a possibility of having misconfigured DHCP servers that allows fully-qualified domain name of RMI server machines. RMI client in this case try to access the outside server's DHCP domain that will make it unavailable for the server.

There is a possibility of having the error due to WINS server. It is possible that only registered users might not be reachable by hosts.

There is a possibility of having a firewall that is blocking the RMI client and server side requests. If the server resides inside the firewall and the client outside then the client won't be able to make any remote calls to the server that is inside due to the firewall.