Doubt with towiresorted

[Kevin Darcy]

On 7/1/2011 2:40 AM, Vignesh Gadiyar wrote:
> I have created a static zone file for "www.abcd.com 
> <http://www.abcd.com>" with the Answer section entries 

Hold it right there. A zone file doesn't contain "answer sections", it 
contains zone data. That's an important, fundamental distinction. 
"Answer sections" sometimes form part of "responses", which are produced 
through the name-resolution process/algorithm, and then rendered in 
"wire format" for passing back to the client. Hopefully you understand 
both the differences and interrelationship of a nameserver's "private" 
data structures and data storage mechanisms, on the one hand, and, on 
the other hand, the standards-defined network protocol for sending bits 
and bytes of data between the server and the client. Any given RRset is 
going to be formatted differently, depending on whether it's in text 
form in a zone file (defined by standard), held in binary form in some 
sort of organized data structure in volatile memory while named is 
running (proprietary to BIND), or "on the wire" being passed between a 
nameserver and one of its clients (also defined by standard).

> containing 2 IP addresses like 1.1.1.1 and 2.2.2.2. I tried to print 
> these addresses in the towiresorted function for the random order like ->
>
> for(i=0;i<count;i++)
> {
>                 char adstr[40];
>                 isc_uint32_t ip_host=(*(isc_uint32_t 
> *)sorted[i].rdata->data);
>                 inet_ntop(AF_INET,&(ip_host),adstr,adstr,40);
>                 printf("%s  \n",adstr);
> }
>
>
> thinking that rdata->data contains the IP addresses of the answer 
> section. But i am getting different IP addresses when i'm running 
> named and using dig www.abcd.com <http://www.abcd.com>. Some help as 
> to what exactly stores the IPs contained in the Answer section would 
> be really great.
towiresorted() is just an internal BIND conversion function, and the 
product of towiresorted() would *not* be suitable, I don't think, for 
feeding directly to inet_ntop(), since inet_ntop() won't be able to 
handle DNS-style label compression (it doesn't have the whole context of 
the response packet, so how could it?).

What exactly are you trying to do here?

If you just want a program to read a text file containing IP addresses 
and then spit them out in random order, then that's not even DNS-related 
and you don't need BIND libraries for that. Heck, you could just use the 
"sort" command.

If you're trying to query some particular DNS name and then present the 
results in random order, then I think the modern algorithm -- although I 
haven't done any network programming in C for years now -- would be to 
call getaddrinfo(), which will return a linked list of addrinfo 
structures. Parse through that linked list and randomize to your heart's 
content. Please understand, however, that the vast majority of DNS 
resolver implementations will *already* randomize the results (with a 
notable exception being Windows' default, but de-configurable behavior 
of "subnet prioritization"), so re-randomizing in a client program may 
be wasted effort.

                                                                         
                                     - Kevin
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