ntpdate [3912] : aucun serveur adapté à la synchronisation n'a été trouvé

J'ai configuré ntpd sur une installation CentOS avec un simple /etc/ntp.conf avec seulement 3 lignes : 

server 0.pool.ntp.org
server 1.pool.ntp.org
server 2.pool.ntp.org
server 192.168.1.1

Malheureusement, quel que soit l'hôte contre lequel je cours, je ne peux pas synchroniser correctement ntpdate avec un serveur externe. Voici la sortie de débogage que j'obtiens lorsque je l'exécute: 

[root@myhost superuser]# ntpdate -d pool.ntp.org
 3 May 12:23:31 ntpdate[3912]: ntpdate 4.2.4p8@1.1612-o Fri Feb 22 11:23:28 UTC 2013 (1)
Looking for host pool.ntp.org and service ntp
host found : 173.44.32.10
transmit(173.44.32.10)
transmit(69.41.163.31)
transmit(18.85.44.118)
transmit(65.182.144.36)
transmit(173.44.32.10)
transmit(69.41.163.31)
transmit(18.85.44.118)
transmit(65.182.144.36)
transmit(173.44.32.10)
transmit(69.41.163.31)
transmit(18.85.44.118)
transmit(65.182.144.36)
transmit(173.44.32.10)
transmit(69.41.163.31)
transmit(18.85.44.118)
transmit(65.182.144.36)
transmit(173.44.32.10)
transmit(69.41.163.31)
transmit(18.85.44.118)
transmit(65.182.144.36)
173.44.32.10: Server dropped: no data
69.41.163.31: Server dropped: no data
18.85.44.118: Server dropped: no data
65.182.144.36: Server dropped: no data
server 173.44.32.10, port 123
stratum 0, precision 0, leap 00, trust 000
refid [173.44.32.10], delay 0.00000, dispersion 64.00000
transmitted 4, in filter 4
reference time:    00000000.00000000  Thu, Feb  7 2036  1:28:16.000
originate timestamp: 00000000.00000000  Thu, Feb  7 2036  1:28:16.000
transmit timestamp:  d52e6306.7c9cb981  Fri, May  3 2013 12:23:34.486
filter delay:  0.00000  0.00000  0.00000  0.00000 
         0.00000  0.00000  0.00000  0.00000 
filter offset: 0.000000 0.000000 0.000000 0.000000
         0.000000 0.000000 0.000000 0.000000
delay 0.00000, dispersion 64.00000
offset 0.000000

server 69.41.163.31, port 123
stratum 0, precision 0, leap 00, trust 000
refid [69.41.163.31], delay 0.00000, dispersion 64.00000
transmitted 4, in filter 4
reference time:    00000000.00000000  Thu, Feb  7 2036  1:28:16.000
originate timestamp: 00000000.00000000  Thu, Feb  7 2036  1:28:16.000
transmit timestamp:  d52e6306.afcfee21  Fri, May  3 2013 12:23:34.686
filter delay:  0.00000  0.00000  0.00000  0.00000 
         0.00000  0.00000  0.00000  0.00000 
filter offset: 0.000000 0.000000 0.000000 0.000000
         0.000000 0.000000 0.000000 0.000000
delay 0.00000, dispersion 64.00000
offset 0.000000

server 18.85.44.118, port 123
stratum 0, precision 0, leap 00, trust 000
refid [18.85.44.118], delay 0.00000, dispersion 64.00000
transmitted 4, in filter 4
reference time:    00000000.00000000  Thu, Feb  7 2036  1:28:16.000
originate timestamp: 00000000.00000000  Thu, Feb  7 2036  1:28:16.000
transmit timestamp:  d52e6306.e3031a51  Fri, May  3 2013 12:23:34.886
filter delay:  0.00000  0.00000  0.00000  0.00000 
         0.00000  0.00000  0.00000  0.00000 
filter offset: 0.000000 0.000000 0.000000 0.000000
         0.000000 0.000000 0.000000 0.000000
delay 0.00000, dispersion 64.00000
offset 0.000000

server 65.182.144.36, port 123
stratum 0, precision 0, leap 00, trust 000
refid [65.182.144.36], delay 0.00000, dispersion 64.00000
transmitted 4, in filter 4
reference time:    00000000.00000000  Thu, Feb  7 2036  1:28:16.000
originate timestamp: 00000000.00000000  Thu, Feb  7 2036  1:28:16.000
transmit timestamp:  d52e6307.16364db7  Fri, May  3 2013 12:23:35.086
filter delay:  0.00000  0.00000  0.00000  0.00000 
         0.00000  0.00000  0.00000  0.00000 
filter offset: 0.000000 0.000000 0.000000 0.000000
         0.000000 0.000000 0.000000 0.000000
delay 0.00000, dispersion 64.00000
offset 0.000000

 3 May 12:23:36 ntpdate[3912]: no server suitable for synchronization found
demandé sur