Problem with ddns updates

[stefan novak]

Hello again!

I've got a Problem wir ddns updates. I want that cable modems from my
cisco ubr register with ddns.

my config as follow:

ddns-update-style interim;
ddns-updates on;

key DHCP_UPDATER {
        algorithm hmac-md5;
        secret ***secret***;
};

zone cablemodem.net. {
        primary 195.230.160.10;
        key DHCP_UPDATER;
}

zone 31.62.10.in-addr.arpa. {
        primary 195.230.160.10;
        key DHCP_UPDATER;
}

host testmodem2 { hardware ethernet 00:22:3A:DC:36:49; fixed-address
10.62.31.3; filename "test2.cm";
                    ddns-hostname "testmodem2";
                    ddns-domainname "cablemodem.net.";
                    option host-name "testmodem2";
                    option domain-name "cablemodem.net.";
}

subnet 10.62.31.0 netmask 255.255.255.0 {
        option routers 10.62.31.1;
        option broadcast-address 10.62.31.255;
        option time-servers 172.55.55.55;
        ddns-domainname "cablemodem.net.";
}

the bind name server is also configured correctly and i can make an
update via nsupdate cmdline.
the problem is that i don't see an update from the dhcpd server to the
bind server. only when i connect a client behind the cable modem ddns
updates are sent, which is usual not what i want :(

thans for your help,
kind regards Stefan