[CentOS] NTP server problem behind firewall

Giles Coochey giles at coochey.net
Tue Sep 4 04:36:27 EDT 2012


On 04/09/2012 07:31, Artifex Maximus wrote:
>
> The first time (16:39:13.653674) client cannot sync to the server but
> second time (16:39:43.145984) that was successful even if there is a
> 'bad udp cksum'. BTW, is it normal? Tcpdump says there was traffic and
> sync happened later so rule is OK I think.
>
> When tried later sync needs three tries for success. Other time needs
> only one. Might depend on Moon phase. It looks like I have some
> network equipment related problem as well. Therefore I have to talk
> with some Cisco expert.
>
> At the moment I have problem with rsyslogd because there is no log of
> denied packets but that is another story. :-)
>
> Thanks for all of your help!
>
>
Without seeing the full timeline of events, you should bear in mind that 
there will be a gap between the time that an NTP server is started 
before other clocks are allowed to sync to it. This makes sense as you 
wouldn't want to sync time to a source that itself isn't reliable. Once 
the NTP server fulfils some criteria and believes it's clock to be 
reliable, it will allow other systems to sync to it.

-- 
Regards,

Giles Coochey, CCNA, CCNAS
NetSecSpec Ltd
+44 (0) 7983 877438
http://www.coochey.net
http://www.netsecspec.co.uk
giles at coochey.net




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