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

[p vixie]

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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