serial number format in dynamic dns update

Ketil Froyn isc_bind at
Thu Oct 7 11:59:13 UTC 2004

On Thu, 2004-10-07 at 12:15, saravanan ganapathy wrote:
> Hai,
>   RFC suggests that serial number in SOA, should be in
> the format of YYYYMMDDnn. 
> How dyn.dns updates the serial number using this
> format? 
> What is the next serial number using dyndns update, if
> the current serial number is '2004103199'?

An update to BIND adds 1 to the serial number, so the next number would
be 2004103200. Encoding a date in the serial number is just something
people do, and if the serial number were limited to the date format, you
would only be allowed to do 100 updates per 24 hours, which seems like a
somewhat arbitrary and unnecessary limitation.

For details on serial number arithmetic, see RFC1982:

For details on DNS UPDATE, see RFC2136, and specifically section 3.6 on
autoincrementing the serial number on updates:

The RFCs don't say that the server should add 1 on each update, but if
you want it to add something different, you can just include the new
serial you want in each update. As long as it increases (in the sense 
defined in RFC1982), it shouldn't make any difference.

I'm not sure which RFC says the format SHOULD(?) be YYYYMMDDnn, but I'll
guess that it is just a suggestion, and if it isn't, it is deprecated.

Ketil Froyn
ketil at

More information about the bind-users mailing list