inside the mind of a linux admin

DNS Zones and Serial Numbers 101

Recently, there’s been a few instances I’ve come across where DNS updates have been “stuck” or broken due to people screwing up the zone serial numbers. The fields of the zone’s SOA resource record, in particular the “serial number”, determines whether an actual data transfer need occur at all.

The name servers compare the serial number of the SOA resource record on the clusters with the serial number in the last copy of that resource record that it has. If the serial number of the record being transferred is greater (numerically), the data in the zone are deemed to have “changed” (in some fashion) and the name servers proceeds to request the actual zone data transfer from the clusters and propagates the update.

The format in which I use (and 99% of the internet as well) is based on the following format: YYYYMMDDnn

YYYY = year
MM = month
DD = day
nn = revision number

For sanity purposes, this helps us better determine when the last change was made, but more importantly tells the name servers to pull the changes made from the respective name server. If you are unsure of the format, please ask a senior admin or simply increase the last digit in the revision number incrementally by one.

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