<div dir="ltr"><div>Didn't we discuss this recently?</div><div><br></div><div>I assume this is the Cogent<->Hurricane Electric IPv6 peering issue. See the long thread that starts here (short summary: dnsviz is singly homed to HE so can't reach Cogent IPv6 servers):</div><div><br></div><div><a href="https://lists.dns-oarc.net/pipermail/dns-operations/2019-October/019276.html">https://lists.dns-oarc.net/pipermail/dns-operations/2019-October/019276.html</a><br></div><div><br></div><div>Shumon.</div><div><br></div><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Feb 3, 2020 at 3:14 PM SM <<a href="mailto:su@elandnews.com">su@elandnews.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hello,<br>
<br>
<a href="http://c.root-servers.net" rel="noreferrer" target="_blank">c.root-servers.net</a> (2001:500:2::c) is not responding to queries over IPv6 [1].<br>
<br>
Regards,<br>
-sm<br>
<br>
1. The error from DNSViz is "arpa zone: The server(s) were not <br>
responsive to queries over UDP. (2001:500:2::c)"<br>
<br>
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</blockquote></div></div>