[ntp:questions] Ntpd show strange results when only one local server is set

[Prunk Dump]

Hello,

On my network I don't really need an accurate time but I need to all
my hostd are synced to the same server to get Kerberos working.

So I try to setup a central local ntp server and remove all other ntp trafic.

My server name is "fichdc". On my client everything goes fine if I put
the original 4 servers :

ntp.conf
--------------
server 0.debian.pool.ntp.org iburst
server 1.debian.pool.ntp.org iburst
server 2.debian.pool.ntp.org iburst
server 3.debian.pool.ntp.org iburst


But if I add the local server in ntp.conf. Ntpd use my gateway
(172.16.0.1) as a server and stay in a INIT state.

ntp.conf
--------------
server 172.16.0.11 iburst prefer

ntpq -p
--------------
172.16.0.1 .INIT. 16 u - 64  0 0.000 0.000 0.000


And the strange things is that I can't get ntpd working again after
that !!! Even if I reset the ntp.conf config file and restart the ntpd
service many times ! It show always the same output :

ntpq -p
--------------
172.16.0.1 .INIT. 16 u - 64  0 0.000 0.000 0.000

What I'am doing wrong ? Why I can't reset the server ?

My server and the clients are virtualized in Virtualbox. Do you think
that is the origin of the problem ?

Thanks !

Baptiste.