0-TTL when querying "invalid" soa

[Tony Finch]

Tom <tomtux007 at gmail.com> wrote:
>
> We're running BIND-9.12.3-P1 on our authoritative servers and we have the same
> behavior with 0-ttl with a invalid soa-query. Is this bind-specific? Why does
> an invalid soa-record responds with 0-ttl in the authority-section?

Funnily enough, this little obscurity came up elsewhere just last week.

I had the same question back in 2012:

https://lists.isc.org/pipermail/bind-users/2012-June/087843.html

https://tools.ietf.org/html/draft-andrews-dnsext-soa-discovery

The latter link explains the reason for this odd behaviour.

[ Last week we also discussed an odd bit of text in RFC 1035: "For
example, SOA records are always distributed with a zero TTL to
prohibit caching." But RFC 2181 said you must no longer do that. ]

https://twitter.com/fanf/status/1087708537600569344

Tony.
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