getaddrinfo and TTL
p.mayers at imperial.ac.uk
Sat Aug 4 12:03:47 UTC 2012
On 08/03/2012 05:48 PM, Martin McCormick wrote:
> Can one read the TTL for a given lookup in
I don't believe so.
> Better yet, is there a listing of the entire range of
> values one can read from all the structures?
The getaddrinfo() interface is specified in RFC 3493.
Specific platforms might extend the "struct addrinfo" (maybe?) but AFAIK
most / all implementations just conform to the basic RFC.
> I wrote an application years ago to let us change the
> name of a host. The old code uses zone transfer to pull in the
> whole zone, actually several zones in to a pile of A records. We
> look for the old name, replace it with the new name and then do
> a delete and add.
I don't understand this I'm afraid.
> If getaddrinfo contains this value, the replace
> application can run much faster, just doing one lookup, and the
> new record we write back will keep whatever value we originally
If you want TTL, you will need to use DNS-specific functions like the
res_* API. You need to be sure you are querying the master, otherwise
the TTL will be the one from cache, not the "real" value.
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