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

[Davey Song(宋林健)]

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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