Date: Mon, 22 Feb 1999 17:32:30 +1300 From: "Dan Langille" <junkmale@xtra.co.nz> To: Greg Black <gjb@comkey.com.au> Cc: root@namodn.com, dan@wolf.com, freebsd-questions@FreeBSD.ORG Subject: Re: off-site secondary DNS Message-ID: <19990222043255.PLGP682101.mta1-rme@wocker> In-Reply-To: <19990221021356.7333.qmail@alpha.comkey.com.au> References: <19990220192615.GHON682101.mta1-rme@wocker> of Sun, 21 Feb 1999 08:25:52 %2B1300
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Thanks Greg. This is one of the reasons I advise people to reply to the list instead of just privately. My mistakes are caught this way. Cheers. On 21 Feb 99, at 12:13, Greg Black wrote: > Don't follow this advice: > > > Most people now use a serial number of the form YYYYMMDDHHMM. And the > > refresh rate determines how often the secondary will check the primary for > > a more recent serial number. Here's an example of these values from my > > website: > > > > @ IN SOA mydomain.com. root.freebsd.mydomain.com. ( > > 199902210845 ; Serial > > 3600 ; Refresh > > 300 ; Retry > > 3600000 ; Expire > > 3600 ) ; Minimum > > > > The above shows that I modifed the zone files on 21 Feb 1999 at 08:45. > > As any book on the subject will tell you and as the sources to > the version of named provided with FreeBSD will confirm, this > serial number is contained in a 32-bit integer. (Currently, > it's an "unsigned int", but it's still only 32 bits.) > > This means that the maximum possible value that can be used is > 4294967295, about fifty times smaller than 199902210845. In > fact, since there may be implementations out there using signed > integers, the safe maximum for sensible purposes would probably > be 2147483647. Bear in mind that, even if you do use a system > that stores these serial numbers in a 64-bit integer, other name > servers out there will be using 32-bit values for years and so > simply won't interpret your huge values correctly. The most > likely outcome is that all values greater than 4294967295 will > be quietly truncated so that they become 4294967295, thus > defeating the point of incrementing the serial number. > > And the idea that you might need hundreds or thousands of serial > numbers in a single day is utterly absurd. Even using more than > 10 is pretty weird. However, if you wish to use this date-based > serial number format (which many people do, including me), it's > more than enough to allow four digits for the year, two for the > month, two for the day and two for a serial number on that day > (which allows 100 versions per day). So, for example, the first > serial number that I'd use today would be 1999022100, with the > final 00 gradually cycling up towards 99. Even with signed > 32-bit integers, this still gives you the possibility of 100 > different serial numbers per day until the end of the year 2147. -- Dan Langille The FreeBSD Diary http://www.FreeBSDDiary.com/freebsd To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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