PTR not working...

Justin Pryzby justinpryzby at
Thu Aug 6 21:14:11 UTC 2009

On Thu, Aug 06, 2009 at 05:00:59PM -0400, Alexandre Racine wrote:
> @Justin, you mean like a 3rd DNS server? I was thinking about that
> since one recent RFC recommend that 3 DNS servers within 3 networks
> should be present (primary, secondary, and third).

Not for the same reason as having 2 or 3 servers.

The motivation behind Kevin's suggestion of slaving the parent zone is
to allow reverse resolution from your own network to work when your
uplink is down (and if that record manages to not be cached).

My suggestion (from RFC) was to have the same servers that are
advertized for the parent zone also slave local copies of the
delegated zone ( or 1/ or
..).  The motivation here is to avoid relying on remote, recursive
nameservers following a CNAME delegation when the requested data is a
PTR.  Apparently some (ancient?) implementations didn't do that.  The
ISP nameservers will be answering requests for your PTRs (in addition
to CNAMEs).  PTR requests will typically never make it to your server,
even though it's the master.

It might be best to only reqest that configuration from your ISP if
they support TSIG for the transfer of the slave zone.


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