<div dir="ltr">Hello,<div><br></div><div>We had mail outage which was caused by one of our three recursive caching DNS servers to be answering a query like seen bellow.</div><div><br></div><div>What could explain the fact that this record had zero answers? and why would the cache server, apparently, cache this answer for over 10 hours (until I manually cleared the cache)? A user reported that the cache server was returning AAAA records, but no IPv4, though we dont have an example of such query/response saved. I guess the fact that the server had AAAA record would explain why the bellow response is a <span style="font-family:arial,sans-serif;font-size:13px">NOERROR?</span></div>
<div><br></div><div><div style="font-size:13px;font-family:arial,sans-serif">
➜ ~ dig <a href="http://imap.gmail.com/" target="_blank">imap.gmail.com</a> @<a href="http://141.161.200.201/" target="_blank">141.161.200.201</a></div><div style="font-size:13px;font-family:arial,sans-serif"><br></div>
<div style="font-size:13px;font-family:arial,sans-serif">; <<>> DiG 9.9.2-P1 <<>> <a href="http://imap.gmail.com/" target="_blank">imap.gmail.com</a> @<a href="http://141.161.200.201/" target="_blank">141.161.200.201</a></div>
<div style="font-size:13px;font-family:arial,sans-serif">;; global options: +cmd</div><div style="font-size:13px;font-family:arial,sans-serif">;; Got answer:</div><div style="font-size:13px;font-family:arial,sans-serif">
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34151</div>
<div style="font-size:13px;font-family:arial,sans-serif">;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 4, ADDITIONAL: 5</div><div style="font-size:13px;font-family:arial,sans-serif"><br></div><div style="font-size:13px;font-family:arial,sans-serif">
;; OPT PSEUDOSECTION:</div><div style="font-size:13px;font-family:arial,sans-serif">; EDNS: version: 0, flags:; udp: 4096</div><div style="font-size:13px;font-family:arial,sans-serif">;; QUESTION SECTION:</div><div style="font-size:13px;font-family:arial,sans-serif">
;<a href="http://imap.gmail.com/" target="_blank">imap.gmail.com</a>.<span style="white-space:pre-wrap"> </span>IN<span style="white-space:pre-wrap"> </span>A</div><div style="font-size:13px;font-family:arial,sans-serif">
<br></div><div style="font-size:13px;font-family:arial,sans-serif">;; AUTHORITY SECTION:</div><div style="font-size:13px;font-family:arial,sans-serif"><a href="http://gmail.com/" target="_blank">gmail.com</a>.<span style="white-space:pre-wrap"> </span>94747<span style="white-space:pre-wrap"> </span>IN<span style="white-space:pre-wrap"> </span>NS<span style="white-space:pre-wrap"> </span><a href="http://ns3.google.com/" target="_blank">ns3.google.com</a>.</div>
<div style="font-size:13px;font-family:arial,sans-serif"><a href="http://gmail.com/" target="_blank">gmail.com</a>.<span style="white-space:pre-wrap"> </span>94747<span style="white-space:pre-wrap"> </span>IN<span style="white-space:pre-wrap"> </span>NS<span style="white-space:pre-wrap"> </span><a href="http://ns2.google.com/" target="_blank">ns2.google.com</a>.</div>
<div style="font-size:13px;font-family:arial,sans-serif"><a href="http://gmail.com/" target="_blank">gmail.com</a>.<span style="white-space:pre-wrap"> </span>94747<span style="white-space:pre-wrap"> </span>IN<span style="white-space:pre-wrap"> </span>NS<span style="white-space:pre-wrap"> </span><a href="http://ns4.google.com/" target="_blank">ns4.google.com</a>.</div>
<div style="font-size:13px;font-family:arial,sans-serif"><a href="http://gmail.com/" target="_blank">gmail.com</a>.<span style="white-space:pre-wrap"> </span>94747<span style="white-space:pre-wrap"> </span>IN<span style="white-space:pre-wrap"> </span>NS<span style="white-space:pre-wrap"> </span><a href="http://ns1.google.com/" target="_blank">ns1.google.com</a>.</div>
<div style="font-size:13px;font-family:arial,sans-serif"><br></div><div style="font-size:13px;font-family:arial,sans-serif">;; ADDITIONAL SECTION:</div><div style="font-size:13px;font-family:arial,sans-serif"><a href="http://ns2.google.com/" target="_blank">ns2.google.com</a>.<span style="white-space:pre-wrap"> </span>269064<span style="white-space:pre-wrap"> </span>IN<span style="white-space:pre-wrap"> </span>A<span style="white-space:pre-wrap"> </span><a href="tel:216.239.34.10" value="+12162393410" target="_blank">216.239.34.10</a></div>
<div style="font-size:13px;font-family:arial,sans-serif"><a href="http://ns1.google.com/" target="_blank">ns1.google.com</a>.<span style="white-space:pre-wrap"> </span>269064<span style="white-space:pre-wrap"> </span>IN<span style="white-space:pre-wrap"> </span>A<span style="white-space:pre-wrap"> </span><a href="tel:216.239.32.10" value="+12162393210" target="_blank">216.239.32.10</a></div>
<div style="font-size:13px;font-family:arial,sans-serif"><a href="http://ns3.google.com/" target="_blank">ns3.google.com</a>.<span style="white-space:pre-wrap"> </span>269064<span style="white-space:pre-wrap"> </span>IN<span style="white-space:pre-wrap"> </span>A<span style="white-space:pre-wrap"> </span><a href="tel:216.239.36.10" value="+12162393610" target="_blank">216.239.36.10</a></div>
<div style="font-size:13px;font-family:arial,sans-serif"><a href="http://ns4.google.com/" target="_blank">ns4.google.com</a>.<span style="white-space:pre-wrap"> </span>269064<span style="white-space:pre-wrap"> </span>IN<span style="white-space:pre-wrap"> </span>A<span style="white-space:pre-wrap"> </span><a href="tel:216.239.38.10" value="+12162393810" target="_blank">216.239.38.10</a></div>
<div style="font-size:13px;font-family:arial,sans-serif"><br></div><div style="font-size:13px;font-family:arial,sans-serif">;; Query time: 56 msec</div><div style="font-size:13px;font-family:arial,sans-serif">;; SERVER: 141.161.200.201#53(141.161.200.201)</div>
<div style="font-size:13px;font-family:arial,sans-serif">;; WHEN: Sat Aug 24 16:21:17 2013</div><div style="font-size:13px;font-family:arial,sans-serif">;; MSG SIZE rcvd: 186</div></div><div style="font-size:13px;font-family:arial,sans-serif">
<br></div><div style="font-size:13px;font-family:arial,sans-serif">Thanks a lot,</div><div style="font-size:13px;font-family:arial,sans-serif">Mohamed.</div><div style="font-size:13px;font-family:arial,sans-serif"><br></div>
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