[dns-operations] 答复: DNS forwarder behavior on response with cname

[Davey Song(宋林健)]

Yes. Yes. It is exactly what I expected. I'm wondering it is not necessary that the forwarder re-query the cname to double check the A record. It introduces another RTT delay. 

Davey
> -----邮件原件-----
> 发件人: p vixie [mailto:paul at redbarn.org]
> 发送时间: 2018年12月7日 18:29
> 收件人: Davey Song(宋林健); dns-operations at dns-oarc.net
> 主题: Re: [dns-operations] DNS forwarder behavior on response with cname
> 
> A forwarder is a recursive initiator -- so, like a stub resolver, It should forward
> to a recursive responder. RD will be 1 everywhere. Strictly speaking it should
> not try to follow a cname, since a normal stub would not.
> 
> ----- Original Message -----
> From: "Davey Song(宋林健)" <ljsong at biigroup.cn>
> Sent: 2018-12-07 - 09:06
> To: dns-operations at dns-oarc.net
> Subject: [dns-operations] DNS forwarder behavior on response with cname
> 
> > Hi folks,
> >
> >
> >
> > I noticed my local resolver (set forwarder for . ) send queries for
> > cname after it received a response which contains cname in answer section.
> >
> >
> >
> > For example when I dig A www.youku.com @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 ?
> >
> >
> >
> >
> > I paste the dig and configuration information below:
> >
> >
> >
> > dig @192.168.0.212  <http://www.youku.com> www.youku.com
> >
> > ; <<>> DiG 9.10.0-P2 <<>> @192.168.0.212  <http://www.youku.com>
> > www.youku.com
> >
> > ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17756 ;; flags: qr
> > rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 13, ADDITIONAL: 1
> >
> > ;; OPT PSEUDOSECTION:
> > ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION:
> > ;www.youku.com. IN A
> >
> > ;; ANSWER SECTION:
> >  <http://www.youku.com> www.youku.com. 600 IN CNAME
> > ipv6-aserver-heyi.m.taobao.com.
> > ipv6-aserver-heyi.m.taobao.com. 600 IN CNAME
> ipv6-aserver-heyi.m.taobao.com.
> > gds.alibabadns.com.
> > ipv6-aserver-heyi.m.taobao.com.gds.alibabadns.com. 30 IN A
> > 106.11.186.1
> >
> >
> >
> >
> > Bind 9.10.4:
> >
> >
> >
> > options {
> >
> > allow-recursion { any; };
> > allow-query {
> > any;
> > };
> > };
> >
> > zone "." {
> > type forward;
> > forwarders {
> > 114.114.114.114;
> > };
> > };
> >
> >
> >
> >
> >
> > Best regards,
> >
> > Davey
> >
> > _______________________________________________
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