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In case you need to test your website, there are ways that you can fake the DNS IP lookup to be able to do so. We'll take a look at how that's done.

Can I fake the DNS ip lookup to test my website?

The situation is this: you have a working web site, and you're about to move it or make dramatic changes to it. So you make a copy of the web site at a different ip address, possibly with a different temporary domain name. You make all your changes and then want to test it out using the correct URL - the "real" domain name. How can you do that without actually changing the internet's DNS entry for your domain?

It's not hard at all.

Let's look at the example in more detail. Say you're the proud owner of http://example.com, and it lives on a server at IP address 1.2.3.4. You're about to make major changes to it, so you create a new domain, http://test.example.com on a different server with a different IP address - 1.2.3.5.

After you make your changes, you want (or in come cases you may need) to test the new server at the new address but use the "correct", real name of the site: example.com and not test.example.com.

In other words, you would like to change example.com to point to 1.2.3.5 instead of 1.2.3.4. Ideally, though, you would not want that to be true for everyone. In fact, you want that to be true only for you. While you're testing your new site, you want the world to continue to only see example.com at the old IP address 1.2.3.4.

Enter the "hosts" file in Windows. This text file contains IP-to-name mappings that override DNS. In fact, if Windows finds an entry in the DNS file, then the internet DNS is never even consulted.

The hosts file lives in c:\windows\system32\drivers\etc\hosts (where "c:\windows" is your Windows directory). It's just a text file, and each line that doesn't begin with a "#" character is of the form:

number space name

So for our example, we would edit this hosts file and add the following line:

1.2.3.5 example.com

Now, on our machine only "example.com" will reference the new IP address, 1.2.3.5, instead of whatever DNS has listed.

There are a couple of caveats:

  • You'll need an entry for every and any domain or subdomain you're testing. So for example if you needed to test both "example.com" and "www.example.com", you would create two entries.
  • You must remember to remove the entries from your hosts file after your testing is complete. Remember, the hosts file overrides DNS, so if the real IP address for example.com changes again sometime in the future, this machine will continue to believe it's at whatever IP address is listed in hosts.

If this approach sounds vaguely familiar, it's also a technique used by viruses and spyware. By placing entries into your hosts file, malware writers can redirect you to their sites or prevent you from accessing other sites. And that brings us to a final caveat:

  • A properly configured anti-spyware or anti-virus program may prevent you from making changes to your hosts file. It's safe to temporarily override these programs settings while you perform your test, but be sure to restore their real-rime protection when you're done.

Article C2301 - March 8, 2005 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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15 Comments
lucas
June 6, 2005 11:59 PM

Good trick. I supose it will work well if you have a your own server with a static IP address, but probably will be dificult if your domain is hosted in a shared machine. Any idea for this?

Leo
June 7, 2005 8:36 AM

Definetly works for static IPs. Don't understand how a machine being shared or not (in any of several definiteions of 'sharing') makes a difference though.

workaholic
October 6, 2005 11:14 AM

also useful for looking up the current ip of your domain is this online lookup tool: http://www.dnswatch.info

Karl
October 19, 2005 10:03 PM

Quote:

Remember, the hosts file overrides DNS, so if the real IP address for example.com changes again sometime in the future, this machine will continue to believe it's at whatever IP address is listed in hosts.

EndQuote

This is not true, all over the microsoft website it is said that the DNS is read FIRST and the HOSTS file read SECOND. This is a problem for me because I am trying to give a different IP for a hostname and I am unable to because the hostname is first resolved via DNS so Windows does not bother checking HOSTS.

Marci Weinberger
May 30, 2006 10:34 AM

Excellent article. I'm glad that I found it. Two thumbs up!

Chris
September 29, 2006 9:18 AM

Is there a way to forward the index page to the test site using an html tag?

Abegail
January 18, 2008 3:23 PM

hi i will to know how i can block a website..its meebo.com.

Dave
April 23, 2008 11:37 PM

I can't seem to redirect an IP to an IP in the hosts file. I have a desktop application which references an IP that is no longer valid and I don't have the source code. I want to fake the PC into thinking that the old IP is referring to the new IP.

Say my old IP is 1.2.3.4 and my new IP is 1.2.3.5, I want the host file to say something like this:

1.2.3.5 1.2.3.4

This doesn't work though, any ideas?

Leo
April 27, 2008 12:18 PM

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

What you're trying to do isn't possible. An IP address can't
be mapped to another IP address in that way. The hosts file
is all about mapping *names* to addresses.

I don't know of a solution for your application, short of
trying to patch the binary.

Leo


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Lai
June 5, 2008 9:36 PM

Hi, I would like to know how to do the remotely from hometo office with dynamic IP address. Using RealVNC free edition.

peter
July 20, 2008 10:18 PM

so we can say in short that we can't change our website DNS unless YOU changing you hosting server. thanks leo for the useful article.
http://www.fosdir.com

jinlye
October 6, 2008 4:22 AM

Karl wrote: (quote) This is not true, all over the microsoft website it is said that the DNS is read FIRST and the HOSTS file read SECOND. (end quote)

Never mind the documentation - a 2 minute test shows that the hosts file overrides your DNS server. Try putting microsoft.com or whatever other host name you like in your hosts file with a redirection to some other IP, and then do a NSLOOKUP on that host name. You will see that it goes to the IP you specified in the hosts file, not what your DNS server says. What is confusing though is that even though it got the answer from the Hosts file, NSLOOKUP will say that it got the answer from your DNS server - but it is lying.

Anonymous
May 20, 2009 2:33 AM

hi,
The above article is nice.It gave an details of changing DNS entry for our domain.I collected the ip details from this ip-details.It's having the details of finding the ip address location,domain host search also is there.It is really useful for me.

nick
October 6, 2009 11:12 PM

Hi, I have uploaded my site on two servers. I want to use one as a primary server and the second like a backup in case the first goes off-line. I'm experimenting with the name servers, but it seems to choose servers randomly. I set ns1 & ns2 to first server and ns3 & ns4 to second. Any suggestions?

Port Testing
July 8, 2010 12:28 AM

How can one override a DNS mapping only for a particular TCP port? Continuing with your example, let's say the test site is actually hosted on a specific TCP port 8080, that is, http://test.example.com:8080. How can I now change the mapping in such a way that the requests for http://exmaple.com are mapped to 1.2.3.5:8080?

Is that even possible using /etc/hosts?

Nope. Which ports are used has nothing at all to do with DNS lookups. The hosts file is only about DNS, which in turn is only about mapping names to IP addresses.
Leo
09-Jul-2010

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