reverse dns
October 15, 2008 9:55 AM Subscribe
Is there an easy way for me to check if a domain I don't control has reverse dns and spf setup?
Best answer: Online Resource:
MXToolBox: Diagnostics (for rDNS) and spf.
posted by effigy at 10:05 AM on October 15, 2008 [1 favorite]
MXToolBox: Diagnostics (for rDNS) and spf.
posted by effigy at 10:05 AM on October 15, 2008 [1 favorite]
There's no such thing as reverse DNS for a domain -- reverse DNS exists for IP addresses. Think of it this way:
x.example.com ---> 1.2.3.4 = regular, or "forward" DNS; thus, it makes sense to say "forward DNS exists for example.com", since you're able to look up example.com hostnames and map them to IP addresses.
1.2.3.4 ---> x.example.com = reverse DNS; thus, it makes sense to say "reverse DNS exists for 1.2.3.4", since you're able to look up 1.2.3.4 and map it to a hostname. (Technically, reverse DNS exists for the network address block in which 1.2.3.4 sits, perhaps 1.2.3.0/255.255.255.0.)
So there's no way to see if reverse DNS exists for a domain; rather, reverse DNS might or might not exist for each of the IP addresses which has a hostname within that domain. But since a domain might have hostnames that map to IP addresses in 1,000 different network address blocks, you'd have to check each and every one of those address blocks to see if it has reverse DNS set up appropriately before being able to answer the gist of your question.
posted by delfuego at 9:06 AM on October 16, 2008
x.example.com ---> 1.2.3.4 = regular, or "forward" DNS; thus, it makes sense to say "forward DNS exists for example.com", since you're able to look up example.com hostnames and map them to IP addresses.
1.2.3.4 ---> x.example.com = reverse DNS; thus, it makes sense to say "reverse DNS exists for 1.2.3.4", since you're able to look up 1.2.3.4 and map it to a hostname. (Technically, reverse DNS exists for the network address block in which 1.2.3.4 sits, perhaps 1.2.3.0/255.255.255.0.)
So there's no way to see if reverse DNS exists for a domain; rather, reverse DNS might or might not exist for each of the IP addresses which has a hostname within that domain. But since a domain might have hostnames that map to IP addresses in 1,000 different network address blocks, you'd have to check each and every one of those address blocks to see if it has reverse DNS set up appropriately before being able to answer the gist of your question.
posted by delfuego at 9:06 AM on October 16, 2008
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Then type: set type=txt
Then whateverdomain.com
If there's SPF set up you should see a response like "v=spf1....etc"
To check reverse DNS you can do nslookup whateverdomain.com, get the ip address that it gives you and then type nslookup ip.address and see if it gives you whateverdomain.com
posted by mikesch at 10:01 AM on October 15, 2008