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Old 07-07-2008, 04:31 PM
Guy Boisvert
 
Default how do I find out which nameserver returns a DNS query?

Ken Price wrote:
DIG tells you which server returned the results. Look for the SERVER
line, should be third from the bottom. If you want to query specific
nameservers directly, use dig like this:


dig @ns1.myserver domainname.com
dig @ns2.myserver domainname.com

etc, etc.

-Ken




Hi Ken,

Please do not top post! It makes life harder in mailing lists.


http://www.centos.org/modules/tinycontent/index.php?id=16
(item 2, "Guidelines for CentOS Mailing List posts")


I didn't include the last replies but it's all messed up.


Thanks !


Guy Boisvert, ing.
IngTegration inc.
_______________________________________________
CentOS mailing list
CentOS@centos.org
http://lists.centos.org/mailman/listinfo/centos
 
Old 07-07-2008, 06:03 PM
Ken Price
 
Default how do I find out which nameserver returns a DNS query?

Ok, sorry, let me re-phrase.

I want to know on my own server, which of my nameservers replied to the
DNS query. In this example 4.2.2.1 is our ISP's upstream DNS server,
which is configured in /etc/resolv.conf - so it should technically
appear there.

But, let's say I query host1.myserver.co.za - and myserver.co.za is on
another server, and has ns1.myserver.co.za, ns2.myserver.co.za,
ns3myserver.co.za & ns4.myserver.co.za

So, as far as I know, any one of those can reply (round robbin DNS?),
but I would like to know which one replies for this particular dig. Is
that possible? I don't want to specify a server to query, I want to
find out which of the 4 returns the query. If it's a cached reply, does
it mean I won't see it?

--


Hmm. As far as I know, the only place you can find that information
is on the caching DNS server responding to your queries. If you want
those details, setup your own recursive name server and enable verbose
logging.


Anyone else with ideas?

-Ken


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http://lists.centos.org/mailman/listinfo/centos
 
Old 07-07-2008, 06:37 PM
"nate"
 
Default how do I find out which nameserver returns a DNS query?

Ken Price wrote:

> Hmm. As far as I know, the only place you can find that information
> is on the caching DNS server responding to your queries. If you want
> those details, setup your own recursive name server and enable verbose
> logging.
>
> Anyone else with ideas?

Run tcpdump on the client machine and see which system sends a reply?

$ host www.nasa.gov
www.nasa.gov is an alias for www.nasa.gov.speedera.net.
www.nasa.gov.speedera.net is an alias for www.nasa.gov.edgesuite.net.
www.nasa.gov.edgesuite.net is an alias for a1718.x.akamai.net.
a1718.x.akamai.net has address 216.39.150.135
a1718.x.akamai.net has address 216.39.150.136

# tcpdump -i eth0 -n port 53 | grep nasa
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
11:35:22.345956 IP 216.39.174.24.53 > 209.97.207.48.53: 55994 [1au] A?
www.nasa.gov. (41)
11:35:22.384898 IP 216.39.174.24.53 > 198.116.4.181.53: 5495 [1au] A?
www.nasa.gov. (41)
11:35:22.480205 IP 216.39.174.24.53 > 192.26.92.30.53: 34592 [1au] A?
www.nasa.gov.speedera.net. (54)
11:35:22.582535 IP 216.39.174.24.53 > 63.209.3.131.53: 42385 [1au] A?
www.nasa.gov.speedera.net. (54)
11:35:22.619921 IP 216.39.174.24.53 > 63.209.3.131.53: 42385 A?
www.nasa.gov.speedera.net. (43)
11:35:22.692525 IP 216.39.174.24.53 > 64.211.42.196.53: 27350 [1au] A?
www.nasa.gov.edgesuite.net. (55)
11:35:22.797816 IP 216.39.174.24.53 > 64.211.42.196.53: 27350 A?
www.nasa.gov.edgesuite.net. (44)

My internal name server forces the source port to be 53, so you may not
want to use the port 53 option if your source port is random.

nate

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Old 07-07-2008, 06:46 PM
Guy Boisvert
 
Default how do I find out which nameserver returns a DNS query?

Ken Price wrote:
>> Please do not top post! It makes life harder in mailing lists.
>>
>>
>> http://www.centos.org/modules/tinycontent/index.php?id=16
>> (item 2, "Guidelines for CentOS Mailing List posts")
>>
>>
>> I didn't include the last replies but it's all messed up.
>
>
> Dude. Give me a break. I was just quick-replying and not thinking.
> Reply privately next time.
>
> -Ken

Hi Ken,

I didn't want to be rude or anything. It's just that those top posting
are coming again and again. It makes threads harder to read and the
posting guidelines to the CentOS list are public and well defined.


I thank you for your help. But people have to realize that these
guidelines are not just for fun or temporary. The more people know
about it, the better it is for the sake of the list. That's why i'll CC
to the list, it's good for people that don't know about the guidelines.
Maybe you were not aware of them, now you are and thanks for that.


Regards,


Guy Boisvert, ing.
IngTegration inc.
_______________________________________________
CentOS mailing list
CentOS@centos.org
http://lists.centos.org/mailman/listinfo/centos
 
Old 07-09-2008, 02:17 PM
"Michael Simpson"
 
Default how do I find out which nameserver returns a DNS query?

> Ok, sorry, let me re-phrase.
>
> I want to know on my own server, which of my nameservers replied to the DNS
> query. In this example 4.2.2.1 is our ISP's upstream DNS server, which is
> configured in /etc/resolv.conf - so it should technically appear there.
>
> But, let's say I query host1.myserver.co.za - and myserver.co.za is on
> another server, and has ns1.myserver.co.za, ns2.myserver.co.za,
> ns3myserver.co.za & ns4.myserver.co.za
>
> So, as far as I know, any one of those can reply (round robbin DNS?), but I
> would like to know which one replies for this particular dig. Is that
> possible? I don't want to specify a server to query, I want to find out
> which of the 4 returns the query. If it's a cached reply, does it mean I
> won't see it?
>
>

is "dig +trace host" what you are looking for?
if not then the bind-users mailing list is a fantastic resource for
all dns queries
(pun intended)

mike
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Old 07-09-2008, 02:51 PM
"Brian"
 
Default how do I find out which nameserver returns a DNS query?

On Wed, July 9, 2008 10:17 am, Michael Simpson wrote:
>> Ok, sorry, let me re-phrase.
>>
>> I want to know on my own server, which of my nameservers replied to the
>> DNS
>> query. In this example 4.2.2.1 is our ISP's upstream DNS server, which
>> is
>> configured in /etc/resolv.conf - so it should technically appear there.
>>
>> But, let's say I query host1.myserver.co.za - and myserver.co.za is on
>> another server, and has ns1.myserver.co.za, ns2.myserver.co.za,
>> ns3myserver.co.za & ns4.myserver.co.za
>>
>> So, as far as I know, any one of those can reply (round robbin DNS?),
>> but I
>> would like to know which one replies for this particular dig. Is that
>> possible? I don't want to specify a server to query, I want to find out
>> which of the 4 returns the query. If it's a cached reply, does it mean I
>> won't see it?

At the end of your dig reply you will see the following..

;; Query time: 26 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Wed Jul 9 10:49:40 2008
;; MSG SIZE rcvd: 297

That tells you which server answered the query.

HTH

_______________________________________________
CentOS mailing list
CentOS@centos.org
http://lists.centos.org/mailman/listinfo/centos
 
Old 07-09-2008, 03:07 PM
Rudi Ahlers
 
Default how do I find out which nameserver returns a DNS query?

Brian wrote:

On Wed, July 9, 2008 10:17 am, Michael Simpson wrote:


Ok, sorry, let me re-phrase.

I want to know on my own server, which of my nameservers replied to the
DNS
query. In this example 4.2.2.1 is our ISP's upstream DNS server, which
is
configured in /etc/resolv.conf - so it should technically appear there.

But, let's say I query host1.myserver.co.za - and myserver.co.za is on
another server, and has ns1.myserver.co.za, ns2.myserver.co.za,
ns3myserver.co.za & ns4.myserver.co.za

So, as far as I know, any one of those can reply (round robbin DNS?),
but I
would like to know which one replies for this particular dig. Is that
possible? I don't want to specify a server to query, I want to find out
which of the 4 returns the query. If it's a cached reply, does it mean I
won't see it?



At the end of your dig reply you will see the following..

;; Query time: 26 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Wed Jul 9 10:49:40 2008
;; MSG SIZE rcvd: 297

That tells you which server answered the query.

HTH

________________________________

Hi Brain

I think you have missed a reply on this topic

That's the ISP's DNS server you see there.

dig +trace domain is what I needed

--

Kind Regards
Rudi Ahlers
CEO, SoftDux

Web: http://www.SoftDux.com
Check out my technical blog, http://blog.softdux.com for Linux or other technical stuff, or visit http://www.WebHostingTalk.co.za for Web Hosting stuff

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