Nsupdate and TTL

[Mark Andrews]

> On 23 Apr 2020, at 07:20, Evan Hunt <each at isc.org> wrote:
> 
> On Wed, Apr 22, 2020 at 03:04:38PM -0600, @lbutlr via bind-users wrote:
>> # nsupdate -k /path/to/key
>>> zone example.com
>>> ttl 3600
>>> send
>>> ^d
>> 
>> No errors, but no change in the TTL.
> 
> "ttl 3600" just means "from now on assume I mean ttl 3600 in all the
> records I send". You didn't actually send an update, so nothing changed..
> 
> As far as I can recall, the only way to change a TTL in nsupdate is to
> delete the whole RRset and then add it back in the same transaction:
> 
>> zone example.com
>> ttl 3600
>> update del example.com in a
>> update add example.com in a 192.0.2.1
>> update add example.com in a 192.0.2.2
>> update add example.com in a 192.0.2.3
>> send

Also don’t forget to add a prerequisite section to ensure you are removing
the records you think you are.

zone example.com
ttl 3600
prereq yxrrset example.com in a 192.0.2.1
prereq yxrrset example.com in a 192.0.2.2
prereq yxrrset example.com in a 192.0.2.3
update del example.com in a
update add example.com in a 192.0.2.1
update add example.com in a 192.0.2.2
update add example.com in a 192.0.2.3
send

Also note you can’t do it this way for the NS RRset at top of zone.  You need to
delete the NS RRs individually and then add them back without deleting all the
NS at any point in the process as the NS RRset is required to always exist.

Note: named only keeps a single TTL for a RRset so it will update the TTL on all
the records when you add a new one with a different TTL but this is not part of
the UPDATE RFC.

-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: marka at isc.org