从缓存响应时间慢

Question

我注意到来自Google 8.8.8.8的非常奇怪但一致的性能行为。即使-尽管DNS记录被缓存，响应时间仍在20-30ms的范围内，这似乎很高。当我切换到OpenDNS时，缓存的响应时间下降到了1ms。不用说，刚刚将所有服务器都切换到了OpenDNS。有人能解释一下Google公共DNS的这种糟糕的性能行为吗？

以下是每个测试用例的dig输出：

Google公共DNS

未缓存(389)

➜  ~  dig @8.8.8.8 commando.io

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> @8.8.8.8 commando.io
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 655
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;commando.io.       IN  A

;; ANSWER SECTION:
commando.io.        300 IN  A   192.241.225.51

;; Query time: 389 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Sun Sep 22 12:08:37 2013
;; MSG SIZE  rcvd: 45

缓存(24)

➜  ~  dig @8.8.8.8 commando.io

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> @8.8.8.8 commando.io
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55425
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;commando.io.           IN  A

;; ANSWER SECTION:
commando.io.        295 IN  A   192.241.225.51

;; Query time: 24 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Sun Sep 22 12:08:42 2013
;; MSG SIZE  rcvd: 45

OpenDNS

未缓存(46)

➜  ~  dig commando.io 

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> commando.io
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 49578
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;commando.io.       IN  A

;; ANSWER SECTION:
commando.io.        300 IN  A   192.241.225.51

;; Query time: 46 msec
;; SERVER: 208.67.222.222#53(208.67.222.222)
;; WHEN: Sun Sep 22 12:09:43 2013
;; MSG SIZE  rcvd: 45

缓存(1ms)

➜  ~  dig commando.io

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6_4.6 <<>> commando.io
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42532
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;commando.io.       IN  A

;; ANSWER SECTION:
commando.io.        273 IN  A   192.241.225.51

;; Query time: 1 msec
;; SERVER: 208.67.222.222#53(208.67.222.222)
;; WHEN: Sun Sep 22 12:10:10 2013
;; MSG SIZE  rcvd: 45

Answer 1

这可能与邻近程度有关，而不是任何事情-- 1ms的响应时间表明您正在访问的OpenDNS服务器从路由角度看非常接近您的系统。

DNS查询时间与原始往返时间(ping)相比如何？