[dns-operations] Maximum TTL limits on public resolvers

Winfried Angele abang at t-ipnet.net
Sun Nov 14 07:41:36 UTC 2021



Am 14. November 2021 01:29:06 MEZ schrieb Sadiq Saif <lists at sadiqsaif.com>:
>Hi all,
>
>While doing some checks on records in my zones I noticed that two public resolvers limit maximum TTL values. Google Public DNS limits to six hours and Quad9 limits to twelve hours. I tested this with a freshly created A record to forgo the possibility of caching. The actual TTL of the record at the authoritative servers is twenty four hours.
>
>What is the technical or other reason(s) for such TTL limiting?
>

I suspect the resolvers operators want to reduce the impact of wrong RRs. Not every zone operator thinks about reducing the TTLs before changes. It is a compromise.

Winfried



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