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</o:shapelayout></xml><![endif]--></head><body lang=ZH-CN link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span lang=EN-US style='font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D'>Hi Liang Rong<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D'>the resolver should do with the first way you mentioned.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D'>Resolver should keep the query clients in one list, then send the related queres to authoritative servers if the answer can't be found in local caches,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D'>and a fail(Server Fail) answer should send back to the query clients if the resolver still can't get the final answer after a fixed time(the default time of bind9 is 30s)<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D'>Likun zhang<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.5pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div style='border:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 4.0pt'><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:宋体'>发件人<span lang=EN-US>:</span></span></b><span lang=EN-US style='font-size:10.0pt;font-family:宋体'> bind10-dev-bounces+zlkzhy=gmail.com@lists.isc.org [mailto:bind10-dev-bounces+zlkzhy=gmail.com@lists.isc.org] </span><b><span style='font-size:10.0pt;font-family:宋体'>代表 </span></b><span style='font-size:10.0pt;font-family:宋体'>荣亮<span lang=EN-US><br></span><b>发送时间<span lang=EN-US>:</span></b><span lang=EN-US> 2014</span>年<span lang=EN-US>3</span>月<span lang=EN-US>31</span>日<span lang=EN-US> 17:41<br></span><b>收件人<span lang=EN-US>:</span></b><span lang=EN-US> bind10-dev@lists.isc.org<br></span><b>主题<span lang=EN-US>:</span></b><span lang=EN-US> [bind10-dev] What's the mechanism for recursive query<o:p></o:p></span></span></p></div></div><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><div><p class=MsoNormal><span lang=EN-US>Hi BIND hackers,<o:p></o:p></span></p><div><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US>I'm using BIND to provision the DNS service. Now, I have a concern about the mechanism of recursive query when a DNS server can not resolve the client query locally. My question is described below.<o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US>The client sends query to the preferred DNS sever (which is using BIND for DNS service), and unfortunately the preferred DNS server can't resolve the query locally. I can imagine following two methods for how to do recursive queries to root/authoritative DNS servers.<o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US>1) The preferred DNS server queued the client query packets and send recursive queries to root/authoritative DNS servers immediately. After an authoritative response obtained, the preferred DNS server returns response the right client in the queue.<o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US>2) The preferred DNS server silently discards the client query packet but immediately sends recursive queries to root/authoritative DNS servers. The client may send queries to the preferred DNS server periodically in certain interval before it is resolved. There will be a time window for the preferred DNS server do recursive queries and receive responses from root/authoritative DNS servers. The preferred DNS server doesn't need to store client query information and only replies to the client when a resource record is found in the local cache. The client query is resolved after the second query.<o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US>Who can tell me which is the right method for recursive query when the preferred DNS server can't resolve query locally? Or if there is another method? Thanks in advance.<o:p></o:p></span></p></div><div><div><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p></div><p class=MsoNormal><span lang=EN-US>-- <br><br>Liang Rong <o:p></o:p></span></p></div></div></div></div></body></html>