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<div class="moz-cite-prefix">On 2024-10-23 1:38 AM, Peter Thomassen
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:26d4bb35-9161-4be2-b4a0-0afa87da22ee@desec.io">CAUTION:
This email is from an external source. Be careful when clicking
links or opening attachments.
<br>
<br>
Hi Mark,
<br>
<br>
On 10/23/24 01:16, Mark E. Jeftovic wrote:
<br>
<blockquote type="cite">But most providers do it via CNAME
flattening, so at the end of the process, they aren't really
CNAMEs, they're A recs.
<br>
<br>
But this will not work for Substack custom domains - and after
going back and forth with their support, who took it up with
some ops, it turns out that custom domains /at the apex/ on
Substack will /only work/ when the query returns, literally, a
CNAME when queried.
<br>
</blockquote>
<br>
Hm, so why is that?
<br>
<br>
From Substack's web server perspective, the client is making an
HTTP request to their IP address, and it does not matter (in fact,
the web server does not know) whether that IP address is looked up
from a CNAME or via an A record directly. In the latter case, it
also does not matter whether that A record is maintained manually
or automatically (via CNAME flattening).
<br>
<br>
</blockquote>
<br>
<p>I believe it's because <b>target.substack-custom-domains.com</b>
runs on Cloudflare CDN and they either need the custom domain to
be <i>on Cloudflare</i> nameservers or implemented the same way
as Namecheap (which the original email email outlined).</p>
<p>Presumably if its the former, it's because CF can then use some
internal mapping to know which custom domains are in use, for the
latter, well, that's why I asked. It shouldn't make a difference,
because the resolver should just re-query the CNAME target and
wind up with A/AAAA recs anyway (right?)<br>
</p>
<p>After I sent the original message I realized that the example
domain name Substack support gave me, doesn't even map to a custom
domain there, it just redirects to main substack page, so now I'm
wondering if perhaps I'm still not getting a totally accurate
explanation from Substack.</p>
<p>- mark<br>
</p>
<div class="moz-signature"><br>
</div>
<div class="moz-signature">-- <br>
Mark E. Jeftovic <a class="moz-txt-link-rfc2396E" href="mailto:markjr@easydns.com"><markjr@easydns.com></a><br>
Co-founder & CEO easyDNS Technologies Inc.<br>
+1-(416)-535-8672 ext 225<br>
<br>
<small><i>"Never expect a thing you do not want,<br>
and never desire a thing you do not expect."<br>
-- Bob Proctor </i></small></div>
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