Configuring different TTLs in multiple RRs for the same domain name, TYPE, and CLASS

[Barry Margolin]

In article <mailman.443.1458836315.73610.bind-users at lists.isc.org>,
 Ben Bridges <bbridges at springnet.net> wrote:

> TXT records are multiple-purpose.  They can be used for SPF records, Office 
> 365 "MS" records, DMARC records, or whatever arbitrary uses someone dreams 
> up, all for the same domain name.  Microsoft wants a short TTL for their 
> Office 365 records, but I would prefer to generally use a longer TTL for most 
> records (including other TXT records) in order to reduce the query load on 
> our servers.  It would be nice to be able to set a short TTL for the Office 
> 365 record but a longer TTL for other TXT records for the same domain name.

The problem with this is that when the Office 365 records expire and are 
removed from the cache, but the other records have not, the server will 
not know that it should re-query for the O365 records. It still has TXT 
records in its cache, and it will return them in response to a query.

It won't go back to the authoritative server until ALL the TXT records 
expire. During the period between the short TTL and the longest TTL, it 
will be as if the short-TTL records don't exist at all.

-- 
Barry Margolin
Arlington, MA