DDNS TTL in 4.3

Doug Barton dougb at dougbarton.email
Wed Apr 22 21:45:59 UTC 2015

On 4/22/15 3:17 AM, Tony Finch wrote:
> Doug Barton <dougb at dougbarton.email> wrote:
>> In 4.2 and previous it was true that the TTL sent for DDNS requests was 1/2
>> the default lease time. In 4.3 it seems that there is no TTL value sent, so
>> the DDNS records simply inherit the zone default TTL.
> The DNS UPDATE protocol does not allow you to omit the TTL so this
> explanation cannot be right! Also the zone default TTL is just an
> abbreviation allowed by the master file format, and it doesn't exist
> in other parts of the DNS protocol.
> I think what you are observing is that isc-dhcp by default caps the TTL to
> one hour, which happens to be the same as your default TTL.
> There is an item in the release notes:
> https://source.isc.org/cgi-bin/gitweb.cgi?p=dhcp.git;a=blob;f=RELNOTES;hb=HEAD#l683
> and a helpful comment in the source code:
> https://source.isc.org/cgi-bin/gitweb.cgi?p=dhcp.git;a=blob;f=server/ddns.c;hb=HEAD#l345

Thanks Tony!

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