make the client to send host name

[kalyanasundaram S]

How do i make the client to send its host name to dhcpserver so that it gets updated in ddns.
Till now i was using the host declaration like
host test {
  hardware wthernet 00:11..
  ddns-hostname "testmachine";
}

but i dont want this declaration i want to update the original host name of the client in ddns.
It is not getting updated.

how do i do ?
thanks in advance,
  -"kalyan"