Per Hedeland wrote: > In article <[EMAIL PROTECTED]> [EMAIL PROTECTED] (Danny > Mayer) writes: >> James Cloos wrote: >>> Wolfgang> DNS refresh and expire are two SOA entities that are meant to be >>> Wolfgang> looked at by the secondaries of a domain. >>> >>> I'm sure he was thinking of the Time To Live (TTL) values for the >>> individual RRs, rather than the values in the SOA. >> Those are of course not the ones you need to look at since those have to >> do with the zone itself and not the zone records each of which has its >> own TTL. > > I think you misread... "the Time To Live (TTL) values for the individual > RRs" are of course prcisely the ones you need to look at. >
That's what I said. >>> I'm not aware of any universal way to get that at the application level, >>> using the system resolvers. > > Universal it may not be, but using the res_*() functions of the ISC > resolver library (in libresolv.* or integrated into libc depending on > OS) it is of course possible to get at the TTL, since it is included in > the response packet that they provide. Here's a snippet from the DNS > component of FreeBSD's gethostbyname() implementation: > > class = _getshort(cp); > cp += INT16SZ; /* class */ > if (qtype == T_A && type == T_A) > _dns_ttl_ = _getlong(cp); > cp += INT32SZ; /* TTL */ > n = _getshort(cp); > gethostbyname() only supports IPv4 so it's not acceptable. It's been a long time since I looked at the res_*() functions since we don't use them in BIND 9 even though they are built on Unix platforms if you want it. > - that _dns_ttl_ variable is actually externally visible, i.e. available > to applications using gethostbyname(), though this is surely not > universal. (And it seems FreeBSD's getaddrinfo() implementation is > entirely disjunct from gethostby*() - it doesn't provide the TTL at all > as far as I can see.) > That's probably because it was a complete redesign. TTL is usually only relevant for nameservers, applications are expected to just make the requests and let the resolver worry about that level of detail. Danny > --Per Hedeland > [EMAIL PROTECTED] _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
