<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hi Paul,<div class=""><br class=""></div><div class="">This is a design choice by PowerDNS, which is defendable: the domain is misconfigured and the RFCs don't clearly which option to take in such a case. Unfortunately, Google and Unbound toke a different option, so when the customer verifies against 8.8.8.8, it will just work. Also unfortunately, PowerDNS took the option of having the return depend on the state of cache, meaning that depending on the order you execute the queries in, you'll get a different result.</div><div class=""><br class=""></div><div class="">I've had long discussions with the core maintainers and discussion makers at PowerDNS, but – for now – they won't change this behaviour.</div><div class=""><br class=""></div><div class="">Kind Regards,</div><div class=""><br class=""></div><div class="">Frank</div><div class=""><br class=""></div><div class=""><br class=""><div class=""><div><br class=""><blockquote type="cite" class=""><div class="">On 28 Aug 2021, at 9:43 AM, Paul Fletcher via Pdns-users <<a href="mailto:pdns-users@mailman.powerdns.com" class="">pdns-users@mailman.powerdns.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta charset="UTF-8" class=""><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">Hello,<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">We are having problems with pdns-recursor when resolving an MX record for a domain whose delegation is partially mis-configured. Whilst that mis-configuration is clearly the trigger for the problem, the behaviour of pdns is tunring a small problem into a big one, when other recursors do not appear to do so.<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">Version:<span class="Apple-converted-space"> </span></span><span style="font-size: 10.5pt; font-family: Roboto; color: rgb(32, 33, 36); background-color: white;" class="">4.5.5</span><span style="font-size: 11pt;" class=""><span class="Apple-converted-space"> </span>(also seen in earlier versions)<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">OS: CentOS7<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">Description of the problem:<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">Initial discovery of NS for the domain gets an answer from gtld-servers. The answer includes:<o:p class=""></o:p></span></div><ul type="disc" style="margin-bottom: 0cm; margin-top: 0cm;" class=""><li class="MsoListParagraph" style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;" class="">4 NS names; two are in the domain itself, and two are in an unrelated zone. TTL=172800<o:p class=""></o:p></span></li><li class="MsoListParagraph" style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;" class="">A records / IP addresses for those 4 names (one per name). TTL=172800<o:p class=""></o:p></span></li></ul><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">Two of the IP addresses are incorrect. The four name servers are cached, as are the four A records.<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">Recursor then goes on to one of the name servers, for which it has a valid IP. (In fact the IP in the A record is for a different one of the name servers to the one which the initial answer said it was for, but it is nevertheless the IP of a valid name server for the domain). It queries the MX record, and gets back a response. The response includes<o:p class=""></o:p></span></div><ul type="disc" style="margin-bottom: 0cm; margin-top: 0cm;" class=""><li class="MsoListParagraph" style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;" class="">The MX record, with TTL=300<o:p class=""></o:p></span></li><li class="MsoListParagraph" style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;" class="">2 NS servers (two of the four which were in the parent response). TTL=1800<o:p class=""></o:p></span></li><li class="MsoListParagraph" style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;"><span style="font-size: 11pt;" class="">A records for those 2 servers. TTL=1800<o:p class=""></o:p></span></li></ul><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">This time the A records are correct. However, whilst recursor replaces the previous NS records in the cache, it does NOT replace the A records. In older versions it says<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">“Accept answer? NO!”<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">In newer versions it says<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">“Removing record in the 3 section”<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">So now if we look up the MX record again after its TTL has expired, recursor correctly identifies the names of the two name servers to use from cache. It then tries to resolve those to IPs, which it does by using the incorrect A records that were cached from the first response. And since they are not accessible, the query times out. Nothing works until the 1800 TTL on the name servers expires, at which point we go back to the start, getting 4 name servers and 4 IPs, two of which work and allow us to resolve the query this one time only.<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">I don’t understand why the recursor accepted and cached the A records which it got in the response from the gtld-servers – even though the two important ones are in a different zone, with nothing to indicate that gtld-servers are authoritative for that zone; but it doesn’t accept the A records from the delegated name server’s response. Is there something we can do to alter this behaviour? If it either accepted them in both cases or rejected them in both cases, everything would work despite the slightly broken initial response. As I say, we don’t see this problem with other recursive resolvers.<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">The domain is<span class="Apple-converted-space"> </span><a href="http://solera.com/" class="">solera.com</a>.<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">Thanks for any pointers.<o:p class=""></o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm; font-size: 12pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 11pt;" class="">Paul<o:p class=""></o:p></span></div></div><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; background-color: rgb(255, 255, 255);" class=""><font size="2" class="">This electronic communication and the information and any files transmitted with it, or attached to it, are confidential and are intended solely for the use of the individual or entity to whom it is addressed and may contain information that is confidential, legally privileged, protected by privacy laws, or otherwise restricted from disclosure to anyone else. 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If you received this e-mail in error, please return the e-mail to the sender, delete it from your computer, and destroy any printed copy of it.</font></span><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">_______________________________________________</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">Pdns-users mailing list</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><a href="mailto:Pdns-users@mailman.powerdns.com" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">Pdns-users@mailman.powerdns.com</a><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><a href="https://mailman.powerdns.com/mailman/listinfo/pdns-users" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">https://mailman.powerdns.com/mailman/listinfo/pdns-users</a></div></blockquote></div><br class=""></div></div><div class=""><div class=""><div dir="auto" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none; word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div dir="auto" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-family: "Avenir Next"; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">Frank Louwers<br class="">PowerDNS Certified Consultant @ <a href="http://Kiwazo.be" class="">Kiwazo.be</a><br class=""><br class=""></div><div style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-family: "Avenir Next"; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><br class=""></div><br class="Apple-interchange-newline"></div></div><br class="Apple-interchange-newline"></div></div></body></html>