Using my primary home computer running Windows XP and Internet Explorer 7 I am unable to connect to the ABC website, or any of its derivatives. I have tried removing all cookies, resetting Internet Explorer, and removing all the ABC.net.au entries in the registry but this has not fixed the problem. Additionally, I also cannot access the website when using Firefox. However, I can access the website on a different computer in the house, which is connected to the same network. My ISP has not been able to provide a solution to this issue.

Since the issue occurs across both Internet Explorer and Firefox, yet does not occur when using a different computer on the same network, it seems that the problem is related to the computer network configuration rather than the specific web browser or your internet connection in general. In particular, the most likely cause is something wrong with the DNS configuration on the computer. DNS stands for domain name system. Every internet connected computer in the world is assigned a unique IP address (for example, 74.125.127.100) which identifies that computer on the internet. However, it would be unrealistic to expect everyone to remember the IP address for all the websites they wish to visit (think about how many website addresses you know, and then consider the trouble you would have remembering all the addresses if you had to remember their IP addresses). To make things easier for humans to remember the addresses of internet servers the DNS system was developed. This maps a friendly domain name (e.g. google.com) to a specific IP address (e.g. 74.125.127.100). Every time you look-up a website on the internet the domain name address which you type into the web browser has to be converted into the IP address, as computer networks do not understand (nor care) about the domain name – they need the IP address to determine the location of the destination server and how to get to that server. If there is a DNS problem on your computer then the mapping between the ABC website and the ABC website’s IP address could be corrupt or incorrect thus preventing the computer from visiting the website.

Normally when you need to complete a DNS query (find the IP address for a particular domain name) your computer will query the DNS server configured on your computer, which is usually your ISP. This DNS server will then return the IP address for the queried domain name. It seems that this process is working correctly on your computer, because you are able to access other websites. As such, we do not want to fiddle with the working DNS configuration. However, this raises the question as to why the DNS queries for the ABC domain name may not be working. Each Windows based computer (in fact, pretty much every operating system) has a HOSTS file (the file is literally called HOSTS with no file extension). This file allows you to manually specify a domain name to IP address mapping. The HOSTS file is more of a relic from the original days of the internet when there was no Domain Name System and each individual host had to maintain their own database for domain name to IP address mappings. The small size of the internet in those days made such a system practical, more so than the millions of internet related hosts now which require a more distributed and scalable system (which is DNS).

Interestingly, the HOSTS file is treated preferentially over other resolution methods such as DNS. This means if you have a domain name to IP address mapping in the HOSTS file that will override any DNS queries. Therefore, if there is a bad mapping for the ABC website in the HOSTS file, that could explain your inability to visit the website. As a first step, we need to check the HOSTS file. Go to the “Start” menu > “Run” and type the following:
%SystemRoot%\system32\drivers\etc\
and click the OK button. Within the folder that opens you should see the HOSTS file. Right-click on the file and select “Open With”. In the Open With window that appears select “WordPad” and click OK. The HOSTS file should open in WordPad. There will be quite a few comments at the top of the file, denoted by the hash # symbol at the beginning of the line. These can be ignored as they are simply comments which are not parsed (checked) when the file is evaluated. You will also notice some example entries relating to acme.com. On closer inspection you will notice that these entries are comments as well (hash symbol at the beginning of the line) so they can be ignored as they are just examples in comments, and are thus not evaluated. You are interested in the entries below the comments. There should be a few standard entries, such as those for localhost and 127.0.0.1. These are fine as they are default entries in the HOSTS file. However, you should check whether there are any entries relating to ABC websites (such as abc.net.au). If there are any such entries, highlight and delete the line (containing the domain name and the IP address). Once you are done, save the file and close. Restart the computer and check whether the problem continues.

While the HOSTS file is always the first candidate you should check when investigating a potential DNS mapping problem, there are also some other possibilities should that not work. First, try visiting the ABC website using the IP address (essentially bypassing the DNS lookup). In your web browser type 202.6.74.117 which should produce the ABC website. If this works, the problem is definitely DNS related as you can access the website through the IP address. Next, we should try a manual DNS lookup to see what IP address is being returned to your computer for the ABC website. Go to the “Start” menu > “Run” and type “cmd” (without the quotes) then click OK. At the command prompt that appears, type “nslookup” (without the quotes) and hit ENTER. You should now be presented with a > prompt. Type “abc.net.au” (without the quotes) and hit ENTER. This will query for the IP address of that domain name. If DNS is working correctly, you should be returned with the correct IP address. In my queries this returned as 202.6.74.117 but you may receive a different IP address depending on whether the ABC servers are load-balancing over multiple servers (each with a different IP address). To check whether the correct IP address is returned take the IP address and type it into your web browser. If that is the correct IP address, the ABC website should appear.

If an incorrect IP address is returned there still seems to be something wrong with the DNS queries. In theory, the only two places that the computer will look for the IP addresses are in the HOSTS file and then do a DNS lookup via the configured DNS servers. As we have discounted the HOSTS file as causing the problem, since the previous check of that file removed any entries for the ABC website, the only other option is something wrong with the DNS lookups via the DNS server. This is quite strange, but still something that we need to verify. Go to the “Start” menu > “Run” and type “cmd” (without the quotes) and click OK. In the command prompt window that appears, type “ipconfig /all” (without the quotes) and click OK. This should output all the network settings for your computer. I assume that the computer is running on cabled Ethernet (i.e. a cable plugged into a switch or router, as opposed to a wireless connection). As such, look under the “Ethernet adapter Local Area Connection” heading for the “DNS Servers” entry. Once that has been found, go to your other computer and repeat the same procedure. Compare the two DNS Servers to check that they are the same. If not, it is likely that the DNS Servers on the problematic computer are incorrect. In this case, I suggest that you try mirroring the settings on the working computer on the problematic computer. To do this, on each computer go to the “Start” menu > “Control Panel” and open the “Network Connections” control panel (you may need to first select the “Network and Internet Connections” category). Right-click on your network connection and select “Properties”. In the window that appears click the “General” tab. Select “Internet Protocol (TCP/IP)” and click the “Properties” button. This will produce the settings. Make sure the DNS settings are the same on both computers. Click OK to save and close the windows. Check whether the problem continues.

However, should you find that the correct IP address is being returned when you attempt the nslookup queries, it seems that there is no DNS problem at this point. This presents a real mystery as to why the website will not load, particularly across different browsers. In this situation we will need to do some more investigating, so please contact me again for further advice.