在我家的互联网连接上，我能够解析大多数域名，但无法解析 cloudfront.net 的任何子域名。
$ dig @8.8.8.8 resolver-identity.cloudfront.net
; <<>> DiG 9.9.5-3-Ubuntu <<>> @8.8.8.8 resolver-identity.cloudfront.net
; (1 server found)
;; global options: +cmd
;; connection timed out; no servers could be reached
但是，我能够在 TCP 上解决它。
$ dig @8.8.8.8 resolver-identity.cloudfront.net +tcp
; <<>> DiG 9.9.5-3-Ubuntu <<>> @8.8.8.8 resolver-identity.cloudfront.net +tcp
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 21121
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;resolver-identity.cloudfront.net. IN A
;; ANSWER SECTION:
resolver-identity.cloudfront.net. 9 IN A 74.125.190.147
;; Query time: 46 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Mon Jun 30 11:26:14 IST 2014
;; MSG SIZE rcvd: 77
可能出了什么问题？如何解决此问题？