Thanks for the response.
I am using the latest stable release which is: c-ares-1.10.0
Is that what I should be using ? Or should I be using the development
version from github.
Regards
Richard
On Wed, May 27, 2015 at 3:07 PM, Ben Greear <greearb_at_candelatech.com> wrote:
> On 05/27/2015 12:02 PM, Richard wrote:
> > Hello:
> >
> > I am sorry if this message is a duplicate. I tried to post this same
> > message a few weeks ago through gmane but I never got a response. I am
> > trying to post again directly via the c-ares mailing list.
> >
> > I am a recent libcares user. I hope this is the right forum to post this
> > question. If not I apologize and please let me know what is the correct
> > forum or mailing list to use.
> >
> > The project I am working on recently switched to use libcares for
> > DNS queries. Prior to that we were using the standard getaddrinfo()
> > (see "man 3 getaddrinfo") for name to ip resolution. With getaddrinfo()
> > we could not specify a timeout value to perform the DNS query. Hence we
> > switched to use libcares.
> >
> > Our use of libcares is getting some stability issues especially if
> > we use wireless network. libcares will sometimes fail to resolve the
> > hostname. Libcares will fail to resolve the hostname within our timeout
> > of 60 seconds.
> >
> > Let me elaborate:
> >
> > - If I do a few DNS queries using libcares then everything is fine.
> >
> > - I wrote a profiling tool that does many DNS queries in a loop. For
> > example, we resolve "www.google.com <http://www.google.com>" and we do
> 100 iterations of that
> > in a loop.
> >
> > - If I run that with my laptop that has a wired connection to my router
> > then everything is fine. Name resolution with libcares is rock solid
> > and it does not fail to resolve www.google.com <http://www.google.com>
> to its IP address for
> > every iteration
> >
> > - If I run that with my laptop that has a wireless connection to my
> > router. Then maybe at the 60th iteration libcares will timeout and not
> > be able to resolve "www.google.com <http://www.google.com>"
> >
> > There must be something I am doing wrong. I am probably using libcares
> > in a way that it is not supposed to be used. I am wondering how other
> > projects such as curl are using libcares.
> >
> > A few things come to my mind:
> >
> > [1] By default libcares makes DNS queries using UDP. Should I use the
> > ARES_FLAG_USEVC to specify libcares to use TCP instead ?
> >
> > [2] Should I implement caching ? At my application level, should I
> > cache the name to ip resolution and don't invoke libcares to make a DNS
> > query. Then this leads to the next question of what timeout should I
> > use to evict old entries from my cache.
> >
> > Once again, I am probably using libcares in a wrong way. So your insight
> > is much appreciated.
>
> I doubt using TCP is a good idea. Maybe cares has issues dealing with
> retransmitting frames, or something like that.
>
> First, make sure you are using the latest libcares.
>
> Then, maybe a network capture that involves a failure would be helpful.
>
> You might also try using 'netem' or some other network impairment tool to
> drop frames (and/or add delay) to reproduce this in a more controlled
> environment.
>
> Thanks,
> Ben
>
>
> --
> Ben Greear <greearb_at_candelatech.com>
> Candela Technologies Inc http://www.candelatech.com
>
>
Received on 2015-05-27