What is the difference between DNS lookup and reverse DNS lookup?

A "reverse lookup" is a function performed by the name servers of the DNS system. When you request a record from a given name server, they should be able to answer that question for you. If they don't answer, it means they don't have the information.

An "A (address) record" is similar, except it's defined on the authoritative name servers of the domain. These are usually set up automatically by the DNS system, however you can change them as well. An example might be www.com, whose A record would be an IP address of 192.168.

What is meant by reverse lookup in DNS?

What does this mean and what is it used for?

In a nutshell, the idea behind reverse lookup is that a given domain name can be resolved to an IP address. In many cases, this happens automatically by using a local DNS server. However, if you have to do the lookup yourself, you have to find out the IP address first. This is done by looking up the name in a DNS database (which is normally just a BIND or DNS cache).

The DNS database contains all records related to a domain, which include everything from the nameserver IP address to the A record for the domain name. When you want to look up a domain name, you simply type in its name and get the information.

There are two main ways of doing this. The first one is looking it up through a DNS server. When you want to look up a domain name, you use a DNS server that has the IP address for the domain in question. When you know the name, you ask the DNS server for the IP address. The DNS server will then reply with the IP address. The domain name was found. This is called forward lookup.

The second way is to look up the domain name using the DNS database directly. This is called reverse lookup. When you type in a domain name into your browser, the DNS server looks up the domain name in the DNS database and returns the IP address.

How do I do a reverse DNS lookup?

You can do the lookup in 3 steps: Lookup the domain name in DNS. Use the standard domain name lookup tools to find the A record for your target domain. You can do this in a number of ways, such as nslookup, dig, host, and others.

Lookup the IP address from the domain name. You can do this by looking up the A record and converting it into an IP address using the reverse of the reverse lookup process. You can do this in a number of ways, such as ipcalc.

Make an outbound connection to the IP address you found in step 2. This may be using either of the above methods or by other means.

The process of using a domain name as an IP address may be broken down into the following steps: First, look up the domain name in DNS. If the IP address is returned, convert the IP address returned from step 1 to a domain name. Look up the domain name from the IP address returned from step 2. In many situations, step 3 can be simplified or avoided entirely. For example, if you have a computer with a fixed IP address, then step 2 can be avoided. Similarly, if you can get the IP address from a known upstream DNS server, step 1 can be skipped.

Step 1 is not trivial, because the domain names returned by DNS records are frequently non-alphanumeric (although they're sometimes encoded to be), and there is no standardized algorithm for how to perform the conversion of one domain name to another domain name. There are also some cases where you cannot even determine which domain name is associated with a particular IP address. This can become more problematic if the IP address is in a different domain. The RFCs governing the DNS protocol specify that they are not intended to serve as directory services. Instead, they are intended to be a mapping between domain names and IP addresses. Therefore, as an implementation detail, the DNS protocol does not specify what to do when you are presented with a domain name for which there is no matching IP address.

Some methods of handling the problem of domains not having corresponding IP addresses are: Do nothing, and treat the missing IP address as if it were actually in use. This is sometimes referred to as "unspecified" or "absent".

Do I need reverse lookup for DNS?

I'm a Windows user, and I use Outlook to send mail. I have no idea what DNS server I use, but I did notice when I sent a message that the MX record (where your domain's mail server is) had the address of the same machine as my email address, which I was not expecting.

That means that the sending machine had already resolved the address of the server to be localhost (127.0.1). I don't know if this was actually the DNS server I was using, but it seems like a big security flaw. I'm not sure how I would configure my DNS server if I wanted to use a reverse lookup so that I could see where my mails were coming from.

2 Answers.
For most purposes, you will not need to do reverse lookups. However, if you use a mail server which you do not control and you have multiple MX records for the same name, you will need to resolve the address of the mailserver to see where the mails are going.

You should get a mail server for free. It is usually the first thing that people do when they get a domain name. If you don't have one, you can get one for free on Google Apps. You can also get a free mailserver on an existing domain name (such as gmail or yahoo.com). If you have an existing domain name, you can buy a free one, but it is usually pretty expensive. If you use Google Apps, you get a free mailserver, but you have to pay for a web space.

Once you have a mailserver, you should add a mail account. You can add an account on your mailserver directly, but if you have a domain name, you can create an account on your registrar's web site and add the MX record for the domain name there. The MX record must point to your mailserver, so make sure you can get to it.

You should get a web server for free. It is usually the second thing that people do when they get a domain name. You can also get a free web server on an existing domain name (such as gmail or yahoo.com).