2018-03-29 14:37:24 +07:00
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# Intro
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xxx
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2018-03-29 16:04:20 +07:00
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RFC1982
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2018-03-29 14:37:24 +07:00
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## SOA Records
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There is only one SOA that is guaranteed to exist on the internet and that
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is the one for the root zone (called '.'). As of 2018, it looks like this:
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```
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. 86400 IN SOA a.root-servers.net. nstld.verisign-grs.com. 2018032802 1800 900 604800 86400
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```
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This says: the authoritative server for the root zone is called
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'a.root-servers.net'. This name is however only used for diagnostics.
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Secondly, nstld@verisign-grs.com is the email address of the zone
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maintainer. Note that the '@' is replaced by a dot. Specifically, if the
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email address had been 'nstld.maintainer@verisign-grs.com', this would have
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been stored as nstld\\.maintainer.verisign-grs.com. This name would then
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still be 3 labels long, but the first one has a dot in it.
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The following field, 2018032802, is a serial number. Quite often, but by
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all means not always, this is a date in proper order (YYYYMMDD), followed by
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two digits indicating updates over the day. This serial number is used for
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replication purposes, as are the following 3 numbers.
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Zones are hosted on 'masters'. Meanwhile, 'slave' servers poll the master
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for updates, and pull down a new zone if they see new contents, as noted by
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an increase in serial number.
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The numbers 1800 and 900 describe how often a zone should be checked for
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updates (twice an hour), and that if an update check fails it should be
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repeated after 900 seconds. Finally, 604800 says that if a master server
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was unreachable for over a week, the zone should be deleted from the slave.
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This is not a popular feature.
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The final number, 86400, denotes that if a response says a name or RRSET
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does not exist, it will continue to not exist for the next day, and that
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this knowledge may be cached.
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