caching-namserver

[Bob Goodwin]

*Tim wrote:*
> *On Wed, 2006-08-23 at 13:39 -0400, Bob Goodwin wrote:
> *
>> *I have observed instances where the initial response time was near 1000 ms,
>> the second in the tens of ms and then subsequent checks would be above 
>> 100 ms?
>> *
> *
> Same here.
>
> *
>> *Initially for host -a google.com:
>> Received 220 bytes from 127.0.0.1#53 in 1047 ms
>>
>> Then a few seconds later:
>> Received 220 bytes from 127.0.0.1#53 in 38 ms
>>
>> Now some hours later:
>> Received 156 bytes from 127.0.0.1#53 in 467 ms
>>
>> Then using dig <dig google.com>
>> ;; Query time: 168 msec
>> ;; SERVER: 127.0.0.1#53(127.0.0.1)
>> ;; WHEN: Wed Aug 23 13:15:23 2006
>> ;; MSG SIZE  rcvd: 148
>>
>> Repeated several times, always 164-168 ms.
>> *
> *
> I've noticed similar sort of things, myself.  Just to be clear, it
> doesn't matter what made the first query (host, dig, etc.).  Once
> something's looked up an address in your nameserver (e.g. web browser)
> it can cache the results for the next thing (e.g. dig).
> *
*Yes I understand that.
*
> *
>
> *
>> *Then here's one I have not visited today, an address Joanne provided the 
>> other day.
>>
>> dig nlzero.com
>> ;; Query time: 3180 msec
>>
>> dig nlzero.com
>> ;; Query time: 244 msec
>>
>> Then the same address using <host -a nlzero.com>
>>
>> Received 122 bytes from 127.0.0.1#53 in 382 ms
>>
>> The correlation between the two methods is not perfect?
>> *
> *
> Various factors are going to mean there's variable delays between
> results (other things your PC is doing at the time, it's not a real-time
> system, and whether a thing works through several other things, in
> sequence, to get its results).
>
> Query goes out (takes time), DNS checks for local data (takes time), DNS
> server may fetch remote data (takes time), DNS server responds (takes
> time), querying program acts on data (takes time).  Quite probably the
> more data returned with a record (i.e. several A records) the longer the
> time reported by dig, though I would expect other things to be a more
> significant variance to the time.  And certainly, if it has to go
> through several remote DNS servers before finding the responses (queries
> root server to find authoritative server for a domain, which then turns
> out to not be authoritative and refers onto another server...), that'll
> take longer.
>
> *
*Yes, but I was getting opinions that the response time should be in the 
single
digit range and that got me off looking for improvement.  I was quite 
happy with
the results I got initially after installing "caching-namserver."  And I 
guess
I still am, it's doing what it's supposed to do ...*
>> *I did try pinging google with the Dell XP box yesterday.
>> The average of three pings was 775 ms
>> *
> *
> That's a different thing, altogether.  You're measuring the time it
> takes for ICMP (usually) traffic to get between their system and yours,
> DNS data may or may not be obtained from the same systems.  And DNS
> traffic is usually UDP (a different scheme, probably with different
> timing issues - depending on all the software systems involved from one
> end to another).
>
> e.g. Here I have several PCs, a few of them have webservers, a few of
> them have DNS servers.  But it's most likely that if you pinged one of
> them, some other PC's DNS server would have provided you with IP address
> to ping.
>
> *
>> *but I don't know how to check the dns response time with Windows?
>> *
> *
> There are dig type of tools for Windows, but I don't know a name to give
> you a search parameter.  A quick search of "dig for windows" produces
> some results, but I know nothing of them to give any recommendation
> (other than to be cautious).
>
> However, remember that, I think, you're mostly looking up the response
> time of the queried DNS server, not the response time of the machine
> asking the question.  If you're not running a DNS server on that Windows
> box, you're probably not going to see the sort of results that you're
> thinking about.
> *
*It appeared that my dns response times were poor and I was beginning to 
think
it was just this old computer.  I knew it would ping 127.0.0.1 in under 
100 µs
so I tried the same thing on the new Dell XP box and found that Windows 
ping
won't display anything smaller than 1.0ms.  So there was no common 
ground there,
that's all I was doing, it seemed there might be an observable 
difference between
a 450 mHz and a 2.8 gHz machine.  There probably is but I couldn't make any
meaningful measurements on the Windows computer.  I really should put a 
Linux
partition in it but it means buying an SATA drive for a computer that I 
don't
use often and it already has more space than I am likely to need.
*
*Many thanks for the help.

BobG

*