If the server is configured to allow client updates, then if the client sends a fully-qualified domain name in the FQDN option, the server will use that name the client sent in the FQDN option to update the PTR record. For exam ple, let us say that the client is a visitor from the "radish.org" domain, whose hostname is "jschmoe". The server is for the "example.org" domain. The DHCP client indicates in the FQDN option that its FQDN is "jschmoe.radish.org.". It also indicates that it wants to update its own A record. The DHCP server therefore does not attempt to set up an A record for the client, but does set up a PTR record for the IP address that it assigns the client, pointing at jschmoe.radish.org. Once the DHCP client has an IP address, it can update its own A record, assuming that the "radish.org" DNS server will allow it to do so.