CODEWITHSUNDEEP
dnsiphostnamemail-serverdig
Rrmm
Rrmm

Reputation: 53

Two hostnames sharing the same IP

I noticed that one of Google's mail servers (alt4.aspmx.l.google.com) points to 74.125.200.26, but when I do a reverse DNS lookup on that IP I see that the hostname associated with it is sa-in-f26.1e100.net. My limited understanding of DNS is that when you have a situation like that, one hostname is an alias of the other, but that's not the case here.

My initial goal was making a Python program that given an IP address and a hostname, returns a boolean answer indicating whether the IP belongs to a mail server of that domain. The algorithm I implemented used dig to search all mail servers of a domain and then tried to match any of them to the hostname associated with the given IP (which I found using dig -x). My program fails with the case I mentioned before. What am I missing?

Sorry for my bad english. Thanks!

Upvotes: 1

Views: 4563

Answers (1)

Dusan Bajic
Dusan Bajic

Reputation: 10889

Many services can run on one server/ipaddress, and many hostnames can resolve to one IP address. In the other direction, one ip address will most often resolve to only one hostname (if it has PTR record at all), and the name will very often be something generic like ip-xx-yy-zz-qq.networkcarrier.net (so unrelated to any of the services that are legitimately running on that server).

Depending on the purpose of your check, perhaps you can just test if the hostname A record points to the required IP address (because your initial requirement is flawed: ip addresses do not belong to domains, they belong to network providers).

(Still, for some purposes, most notably as anti spam measure, there is a use case for checking if ip address resolves to some particular hostname.)

Upvotes: 1

Related Questions