-   Linux - Newbie (
-   -   Why do forward AND reverse lookups? (

veeruk101 03-30-2005 01:52 PM

Why do forward AND reverse lookups?

I've been reading things were it says that you should always do forward AND reverse lookups. What are the reasons for this? Isn't a forward lookup sufficient, and wouldn't a reverse lookup just tell you what you originally started with?

I know doing both is supposed to help verify whether the person you're dealing with is who they say they are or whatever, but how does this all work? Seems cool.


Technoslave 03-30-2005 01:58 PM

Some RFCs, if followed strictly, require that you also have a reverse lookup. Some MTAs will not deliver mail if you have it setup that if the reverse lookup doesn't come back with what the DNS name is saying, or with just a response, then it won't deliver the mail.

Silly things like that. Maybe someone else has a more concrete reason...usually though, I've used it to help me determine what and where the IP came from.

veeruk101 03-30-2005 08:02 PM


Do you know how exactly the process of forward lookups followed by a reverse lookup prevents against fraud or whatever? You're right that some programs would require it, but how does it solve anything? Wouldn't you just get the same thing you started off with after a forward then reverse lookup?

Thanks again.

Technoslave 03-31-2005 10:22 AM

For instance, let's say I spoof a name from where I'm coming from, but it also logs my IP address, granted that can be spoofed too, but in this example it isn't.

So, what you get is someone trying to send you mail from, but their IP address isn't, so the mail server rejects it.

I'm sure there are other programs that use it frequently, but none that I've really come across lately, especially since my IP address at home, I can change the DNS and point it to the IP, but I don't have control of the reverse for it, and I have yet to have any problems sending mail and the like.

It's just one of those things that when it was setup ( the idea of DNS ) that if you have a forward looking address you should also have a reverse.

The place where you can get bind might have some more info ( )

All times are GMT -5. The time now is 02:08 PM.