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</o:shapelayout></xml><![endif]--></head><body lang=ZH-CN link=blue vlink=purple style='text-justify-trim:punctuation'><div class=WordSection1><p class=MsoNormal><span lang=EN-US>Hi folks,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>I noticed my local resolver (set forwarder for . ) send queries for cname after it received a response which contains cname in answer section. <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>For example when I dig A <a href="http://www.youku.com">www.youku.com</a> @my local resolver . It returns two cname RR and A RR in answer section. It is observed that local resolver sent a A query on the first cname : ipv6-aserver-heyi.m.taobao.com. The local resolver response the client only after it got answer from the cname response. It definite introduces a delay in between. Is it normal ? which RFC specify this or is it a implementation consideration? For what purpose ? <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>I paste the dig and configuration information below:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>dig @192.168.0.212 <a href="http://www.youku.com"><span style='color:windowtext;text-decoration:none'>www.youku.com</span></a> <br><br>; <<>> DiG 9.10.0-P2 <<>> @192.168.0.212 <a href="http://www.youku.com"><span style='color:windowtext;text-decoration:none'>www.youku.com</span></a> <br><br>;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17756 <br>;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 13, ADDITIONAL: 1 <br><br>;; OPT PSEUDOSECTION: <br>; EDNS: version: 0, flags:; udp: 4096 <br>;; QUESTION SECTION: <br>;www.youku.com. IN A <br><br>;; ANSWER SECTION: <br><a href="http://www.youku.com"><span style='color:windowtext;text-decoration:none'>www.youku.com</span></a>. 600 IN CNAME ipv6-aserver-heyi.m.taobao.com. <br>ipv6-aserver-heyi.m.taobao.com. 600 IN CNAME ipv6-aserver-heyi.m.taobao.com.gds.alibabadns.com. <br>ipv6-aserver-heyi.m.taobao.com.gds.alibabadns.com. 30 IN A 106.11.186.1 <br><br><br><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Bind 9.10.4:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>options { <br><br>allow-recursion { any; }; <br>allow-query { <br>any; <br>}; <br>}; <br><br>zone "." { <br>type forward; <br>forwarders { <br>114.114.114.114; <br>}; <br>};<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Best regards,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Davey<o:p></o:p></span></p></div></body></html>