Date: Sun, 21 Feb 1999 12:13:56 +1000 From: Greg Black <gjb@comkey.com.au> To: junkmale@xtra.co.nz Cc: root@namodn.com, dan@wolf.com, freebsd-questions@FreeBSD.ORG Subject: Re: off-site secondary DNS Message-ID: <19990221021356.7333.qmail@alpha.comkey.com.au> In-Reply-To: <19990220192615.GHON682101.mta1-rme@wocker> of Sun, 21 Feb 1999 08:25:52 %2B1300 References: <19990220055521.PZWW3226200.mta2-rme@wocker>; from Dan Langille on Sat, Feb 20, 1999 at 06:54:29PM %2B1300 <19990220192615.GHON682101.mta1-rme@wocker>
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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. -- Greg Black <gjb@acm.org> To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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