On 2/6/2013 10:59 AM, [email protected] wrote:
> I am trying to get to know SNTP by doing some
> Winsock programming. In particular, I am using
>
> getaddrinfo("pool.ntp.org", "123", &hints, &gaires);
>
> where hints has been set up to define a socket type
> of SOCK_DGRAM and family of AF_INET.
> As expected, the Internet address returned in
> *gaires does change from time to time.
> But it seems that it often returns the same value
> if I call it again after a short time.
> But if I wait a minute or two then I get a different address.
> What is the rotation mechanism and why doesn't it give me
> a new address every time?
You are likely using a caching DNS server in that PC's
internet configuration?
When the DNs server you are using queries the pool's
DNS servers it will get back up to 4 A records;
{Usually 4, however int he past some zones didn't
have that many servers}
Then your DNS server returns those A records to you;
Caching DNS servers remember the last answer for a period of time,
and just return it the next time you ask them,
instead of doing a new query to the DNS for the pool;
After some time your caching DNS server when asked
for a pool query, will have expired the cached answer,
and will query the pool DNS servers again,
and get another set of 4 A records (likely non-overlapping).
BTW, if you are going to distribute an application with
the ntp pool as a default config,
you're supposed to get a vendor zone?
<http://www.pool.ntp.org/vendors.html>
e.g. Using 0.vendor.pool.ntp.org
... 0.no-place.pool.ntp.org
instead of the root pool.ntp.org
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