I'd like to see an rDNS service, along the lines of;
rdns.opendns.com
Reason being, there doesn't seem to be an easy way for those of us using Windows, and requiring it to be simply "available", much like WhoIs, for scripting and including into web-based applications.
Domain Tools provides this, but charges for it .... and I can't afford their prices (can barely afford my hosting). Robtex provides something similar, but it tends to be slow and out of date, Trusted Source provide it, but again, it's only available via their website, and is very slow.
All the rDNS would do is;
1. Have an IP passed to it 2. Return a list of hostnames resolving to the IP passed
I know it's alot to ask, but I'd love to be able to include it in my free web based service.
4 Comments
rdns.opendns.com
Reason being, there doesn't seem to be an easy way for those of us using Windows, and requiring it to be simply "available", much like WhoIs, for scripting and including into web-based applications.
Domain Tools provides this, but charges for it .... and I can't afford their prices (can barely afford my hosting). Robtex provides something similar, but it tends to be slow and out of date, Trusted Source provide it, but again, it's only available via their website, and is very slow.
All the rDNS would do is;
1. Have an IP passed to it 2. Return a list of hostnames resolving to the IP passed
I know it's alot to ask, but I'd love to be able to include it in my free web based service.
4 Comments
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written by mysteryfcm 610 days ago
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It's not unsolvable by any means, and whilst it's true that a complete resolution system is open to flaws, it's not as complicated as you make it out to be (I'm very familiar with how the DNS system works ;o)).
rDNS is as simple as querying an IP and having it return it's A and CNAME results.
written by Marius Gologan 280 days ago
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"...those of us using Windows"
What's wrong with "nslookup -type=ptr ip_address" which gives you even the answering NS?
Isn't free anymore, somebody hacked it...? Not this one too, come on, please, be serious!
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anyone who offers you this service and tells you it's a complete list is lying to you.
A Quick Lesson In DNS:
to resolve host.example.com to an IP there is a hierarchy followed. the root servers point to the .com servers who point to example.com's servers who give you the IP to host.example.com.
in the other direction, given an IP the delegation works the similarly. the root servers point to the servers that serve the 1st octet of the IP who point to the servers that serve the 2nd octet and so on. the final answer can be whatever the person who controls reverse DNS for that IP wants it to be.
e.g. if i control the PTR record for 1.2.3.4, i could say that 1.2.3.4 is www.opendns.com. www.opendns.com doesn't point to 1.2.3.4.
but that's not what you want to know. you want to know which hostnames point at what IPs. there just isn't a delegation system that exists that would let you arrive at that answer.
IP -> hostname is a 1:1 mapping
hostname -> IP is a 1:many mapping.
all hostnames -> IP is a many:1 mapping with no way to return a complete, accurate answer.
so first we've established there's no way to properly traverse the DNS infrastructure to find the information you want. that only leaves bad hacks left over.
you could query every single possible hostname looking for records that return your IP. that's impossible, see below.
you could dig through the caches of large recursive DNS servers (like the ones OpenDNS runs). that would find entries that people have used in the past. there could be a hostname that points to your IP, but if nobody looked it up it would not be in anyone's cache. somewhere, someone could create a.completely.long.and.never.used.hostname.com pointing at 1.2.3.4, but unless some DNS server cached it when it was looked up (and you have access to the cache) you'd never know about it.
the results would never be complete.
that is, unless it's in the cache or unless you've walked the entire namespace (which is a gigantic amount of hostnames and a time:space problem that would require a cluster of machines and a lot of bandwidth to pull off).
to summarize: the people who sell this service have no way of knowing every hostname that points at a particular IP. they just know the popular hostnames that point at it by whatever means of data collection they use.
if you own the IP you're curious about and want to know under which hostname people have arrived at your website, you could log the Host: header people send when they connect.
in other words, this is an unsolvable solution looking for a problem.