Interaction of CNAME and A records with regard to TTL

Mark_Andrews at Mark_Andrews at
Wed Jan 22 12:07:31 UTC 2003

> Hi,
> thank your for your answers. A follow-up question: how about the TTL of
> CNAME records and the records they point to, is there a constraint that they
> have to be equal? (I assume that not.)


> If not, if the CNAME record expires
> before the records it points to, does the server always resolve those
> records as well and includes them with the response (I assume that it is
> usually the server authoritative for the CNAME is responsible for including
> the records the CNAME points to with the answer)? (I assume yes.)

	It depends if the cannonical name is also served by the server
	that is serving the CNAME.  It also depends if the server is
	offerring recursive service or in recurstive service is requested.

	CNAMES are always followed within the server unless the query type
	is "*" or CNAME.  They are followed off the server if both recursion
	is allowed and requested.

> I saw that
> recursion can be switched off in bind 9 servers even if a client requests
> it.  Does that influence that behavior (fetching the records the CNAME record
> points to)? (I assume it does, that is disables that behavior). How do other
> servers implement this?

	It disables following the query off the server.

	See RFC 1034 for details.
> Another question: The RFC on SRV records explicitly forbids that the rdata
> portion contain an alias. I could not find anything of that kind for NAPTR
> records. Is there a similar restriction on NAPTR records, which I just
> haven't found, or are these two cases handled differently? If yes, does
> anyone know why is that?

	All records should refer to cannonical names.  See RFC 1034.

> Thank you!
> Joachim
Mark Andrews, Internet Software Consortium
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews at

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