Which DNS server Letsencrypt use to verify the dns-01 challenge?

[kevin2seedlink]

I want to integrate Cloudflare API for automate challenge processing.

But after privisioning a TXT record and success checking locally, it always gives me an error
{u’status’: 403, u’type’: u’urn:acme:error:unauthorized’, u’detail’: u’Correct value not found for DNS challenge’}

I use the same way in code to generate keyAuthorization, and it worked for http-01 challenge.
So I’m thinking whether it is caused by DNS record propagation.

I want to know which DNS server(s) letsencrypt use so I can check locally and then request the challenging phrase.

Thanks

[serverco]

It will use your domains authority DNS servers - so if you are using cloudfflare as your primary, authoritative nameservers, it will use those specific ones at cloudflare.