[Unbound-users] The flush command of unbound-control doesn't take effect.

[Hongyi Zhao]

Hi all,

Currently, I use the latest release of unbound 1.5.2 compilled by myself on
the Debian wheezy.  I configured the unbound by some  using some
forward-zone sections in its unbound.conf  file, and let it  listen on the
local 1052 port to listen on for queries.

Now, I want to use the unbound-control tool to do some tests, say, cleaning
some type of record in the cache, say, the A record, by using the following
command:

$ sudo unbound-control -c
/home/werner/software/anti-gfw/anti-DNS-cache-poisoning/final-methods/unbound.conf
flush A

But I failed to clean the cache, please see following for detail:

-------------- begin test ------------------------------
werner at debian:~$ dig -p1052 youtube.com

; <<>> DiG 9.8.4-rpz2+rl005.12-P1 <<>> -p1052 youtube.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 20966
;; flags: qr rd ra; QUERY: 1, ANSWER: 11, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;youtube.com.            IN    A

;; ANSWER SECTION:
youtube.com.        3600    IN    A    173.194.127.40
youtube.com.        3600    IN    A    173.194.127.38
youtube.com.        3600    IN    A    173.194.127.41
youtube.com.        3600    IN    A    173.194.127.35
youtube.com.        3600    IN    A    173.194.127.39
youtube.com.        3600    IN    A    173.194.127.46
youtube.com.        3600    IN    A    173.194.127.37
youtube.com.        3600    IN    A    173.194.127.32
youtube.com.        3600    IN    A    173.194.127.34
youtube.com.        3600    IN    A    173.194.127.36
youtube.com.        3600    IN    A    173.194.127.33

;; Query time: 715 msec
;; SERVER: 127.0.0.1#1052(127.0.0.1)
;; WHEN: Mon Feb 23 10:33:41 2015
;; MSG SIZE  rcvd: 205

werner at debian:~$ sudo unbound-control -c
/home/werner/software/anti-gfw/anti-DNS-cache-poisoning/final-methods/unbound.conf
flush A
ok
werner at debian:~$ dig -p1052 youtube.com
; <<>> DiG 9.8.4-rpz2+rl005.12-P1 <<>> -p1052 youtube.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 22618
;; flags: qr rd ra; QUERY: 1, ANSWER: 11, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;youtube.com.            IN    A

;; ANSWER SECTION:
youtube.com.        3584    IN    A    173.194.127.40
youtube.com.        3584    IN    A    173.194.127.38
youtube.com.        3584    IN    A    173.194.127.41
youtube.com.        3584    IN    A    173.194.127.35
youtube.com.        3584    IN    A    173.194.127.39
youtube.com.        3584    IN    A    173.194.127.46
youtube.com.        3584    IN    A    173.194.127.37
youtube.com.        3584    IN    A    173.194.127.32
youtube.com.        3584    IN    A    173.194.127.34
youtube.com.        3584    IN    A    173.194.127.36
youtube.com.        3584    IN    A    173.194.127.33

;; Query time: 0 msec
;; SERVER: 127.0.0.1#1052(127.0.0.1)
;; WHEN: Mon Feb 23 10:33:57 2015
;; MSG SIZE  rcvd: 205
-------------- end test ------------------------------

 As you can see, after I've done the flush operation  on the A record, the
2nd dig command still can fetech the cached A records -- "the Query time: 0
msec" of the 2nd run of dig should tell this.

Why does this happen?  Could someone please give me some hints?

Regards
-- 
Hongyi Zhao <hongyi.zhao at gmail.com>
Xinjiang Technical Institute of Physics and Chemistry
Chinese Academy of Sciences
GnuPG DSA: 0xD108493
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