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Old 12-04-2009, 01:15 PM
Ryan Chan
 
Default DNS cache in Ubuntu?

Where did the DNS cache being stored in Ubuntu exactly?

Sometime I found the only method to clear the cache is to restart
networking, e.g. sudo /etc/init.d/networking restart



Thanks.

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Old 12-04-2009, 02:33 PM
Chan Chung Hang Christopher
 
Default DNS cache in Ubuntu?

Ryan Chan wrote:
> Where did the DNS cache being stored in Ubuntu exactly?
>
> Sometime I found the only method to clear the cache is to restart
> networking, e.g. sudo /etc/init.d/networking restart
>
>

Is your question related to bind or djbdns? Or is it related to browsers?

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Old 12-04-2009, 03:16 PM
Ryan Chan
 
Default DNS cache in Ubuntu?

On Fri, Dec 4, 2009 at 11:33 PM, Chan Chung Hang Christopher
<christopher.chan@bradbury.edu.hk> wrote:
>
> Is your question related to bind or djbdns? Or is it related to browsers?

Ubuntu network feature, e.g. ping is using old DNS cache.

btw, I found normal user cannot resolve DNS, only root can.

Any right need to set?

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Old 12-04-2009, 04:48 PM
Tom H
 
Default DNS cache in Ubuntu?

>> Is your question related to bind or djbdns? Or is it related to browsers?

> Ubuntu network feature, e.g. ping is using old DNS cache.

Install nscd
aptitude install nscd

To flush
invoke-rc.d nscd restart

> btw, I found normal user cannot resolve DNS, only root can.
> Any right need to set?

Only idea: what are the perms on "/etc/resolv.conf"?

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Old 12-05-2009, 12:38 PM
Ryan Chan
 
Default DNS cache in Ubuntu?

Hello,

On Sat, Dec 5, 2009 at 1:48 AM, Tom H <tomh0665@gmail.com> wrote:
>>> Is your question related to bind or djbdns? Or is it related to browsers?
>
>> Ubuntu network feature, e.g. ping is using old DNS cache.
>
> Install nscd
> aptitude install nscd
>
> To flush
> invoke-rc.d nscd restart
>

I have not installed nscd, so just wonder why caching happen.

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Old 12-05-2009, 01:08 PM
Werner Schram
 
Default DNS cache in Ubuntu?

Ryan Chan schreef:
> Hello,
>
> On Sat, Dec 5, 2009 at 1:48 AM, Tom H <tomh0665@gmail.com> wrote:
>
>>>> Is your question related to bind or djbdns? Or is it related to browsers?
>>>>
>>> Ubuntu network feature, e.g. ping is using old DNS cache.
>>>
>> Install nscd
>> aptitude install nscd
>>
>> To flush
>> invoke-rc.d nscd restart
>>
>>
>
> I have not installed nscd, so just wonder why caching happen.
>
>
The linux kernel does not cache dns queries, you need a userspace
application like nscd for that. If you do not have that installed, your
queries should not be cached. You can check whether you are using a
cache or not by running tcpdump (install via synaptec or apt-get) in one
terminal:

sudo tcpdump -s1024 port domain

and running your ping command in another terminal. If you ping
www.google.com and you get an output similar to this (in the tcpdump
terminal) your queries are not cached:

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 1024 bytes
15:04:30.869872 IP 192.168.1.10.35930 > 192.168.1.1.53: 5192+ A?
www.google.com. (32)
15:04:30.895855 IP 192.168.1.1.53 > 192.168.1.10.35930: 5192 4/0/0 CNAME
www.l.google.com., A 74.125.77.147, A 74.125.77.99, A 74.125.77.104 (100)
15:04:30.925149 IP 192.168.1.10.34416 > 192.168.1.1.53: 33260+ PTR?
147.77.125.74.in-addr.arpa. (44)
15:04:30.959964 IP 192.168.1.1.53 > 192.168.1.10.34416: 33260 1/0/0 PTR
ew-in-f147.1e100.net. (78)
15:04:31.925302 IP 192.168.1.10.46079 > 192.168.1.1.53: 52166+ PTR?
147.77.125.74.in-addr.arpa. (44)
15:04:31.950329 IP 192.168.1.1.53 > 192.168.1.10.46079: 52166 1/0/0 PTR
ew-in-f147.1e100.net. (78)
...

Could you test that?

Werner

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Old 12-06-2009, 11:45 AM
PleegWat
 
Default DNS cache in Ubuntu?

Ryan Chan wrote:
> Hello,
>
> On Sat, Dec 5, 2009 at 1:48 AM, Tom H <tomh0665@gmail.com> wrote:
>>>> Is your question related to bind or djbdns? Or is it related to browsers?
>>> Ubuntu network feature, e.g. ping is using old DNS cache.
>> Install nscd
>> aptitude install nscd
>>
>> To flush
>> invoke-rc.d nscd restart
>>
>
> I have not installed nscd, so just wonder why caching happen.
>

Note the caching may not be happening on your local machine. If you're
using a NAT router it may contain a dns cache, and your ISP will also
have (caching) DNS servers.


$ dig www.google.com

; <<>> DiG 9.6.1-P1 <<>> www.google.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2662
;; flags: qr rd ra; QUERY: 1, ANSWER: 7, AUTHORITY: 4, ADDITIONAL: 4

<snip a lot of answer data>

;; Query time: 25 msec
;; SERVER: 192.168.1.254#53(192.168.1.254)
;; WHEN: Sun Dec 6 13:43:30 2009
;; MSG SIZE rcvd: 284


The lines near the end tell that the query was answered by
'192.168.1.254#53', which is the DNS function of my local NAT router.


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Old 12-06-2009, 07:33 PM
Tom H
 
Default DNS cache in Ubuntu?

>>> Ubuntu network feature, e.g. ping is using old DNS cache.

>> Install nscd
>> aptitude install nscd

>> To flush
>> invoke-rc.d nscd restart

> I have not installed nscd, so just wonder why caching happen.

If you install nscd, clear your local cache, and still have the same
result, you will know that your problem is something else.

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Old 12-07-2009, 05:43 PM
NoOp
 
Default DNS cache in Ubuntu?

On 12/05/2009 06:08 AM, Werner Schram wrote:
> Ryan Chan schreef:
>> Hello,
>>
>> On Sat, Dec 5, 2009 at 1:48 AM, Tom H <tomh0665@gmail.com> wrote:
>>
>>>>> Is your question related to bind or djbdns? Or is it related to browsers?
>>>>>
>>>> Ubuntu network feature, e.g. ping is using old DNS cache.
>>>>
>>> Install nscd
>>> aptitude install nscd
>>>
>>> To flush
>>> invoke-rc.d nscd restart
>>>
>>>
>>
>> I have not installed nscd, so just wonder why caching happen.
>>
>>
> The linux kernel does not cache dns queries, you need a userspace
> application like nscd for that. If you do not have that installed, your
...

I wonder if perhaps it is an avahi issue/problem?
http://www.unchartedbackwaters.co.uk/pyblosxom/tags/dns
<https://bugs.launchpad.net/ubuntu/+source/avahi/+bug/94940>
<https://bugs.launchpad.net/ubuntu/+source/avahi>



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