Disable DNS Lookup On Routers and Servers

disablednslookupA Domain Name System (DNS) is a tool that translates what website address we type into the URL bar into a series of numbers called an IP address. It’s also known as a Domain Name Server or a Domain Number System. DNS exists as a conduit between human language and computer language so that we aren’t having to remember a bunch of numbers to type in for every website we visit; and the server doesn’t have to try and read a bunch of characters it doesn’t understand. The IP address is made up of four sections of numbers separated by periods, it may look something like this: 564.454.458.46. DNS has a database that stores all of this information so that when we use say, Google.com, it can associate what IP address is associated with that site. Once the connection is made, the server can recall all of the data from that site and load it into our web browser. Sometimes there are DNS errors and a site will not load. Learn how to prevent these errors from occurring and what you can do if you’re a little too late in DNS Issues You Didn’t See Coming.

The transfer of information from domain name to DNS database to IP address is called a forward lookup. The DNS can also be used to identify what servers are correct to deliver E-mail and can be used for reverse lookups. A reverse lookup is just a command that converts an IP address back into the proper domain name, like Google.com. The organizational structure of the DNS database resembles a hierarchy. Root name servers are at the top of the DNS and are in charge of maintaining top-level domains like .com or .us. These servers are managed by private businesses and some parties that govern the internet worldwide. There are 13 root name servers that support the plethora of top-level domains that exist on the Internet.

How to Disable DNS Lookup

Under some circumstances, you may not want the DNS to try and lookup the IP address for a mistyped URL, or domain name. The server will end up being non-responsive and it will delay the data from being transferred. What kind of software you are running will determine what course of action you should take to disable the DNS lookup. Cisco is a popular network registrar that provides addressing services for enterprise networks and service providers.

Disable on a Router

If you are using a Cisco router, the steps are pretty straightforward. There is a really great course to help with network troubleshooting that explores Cisco routers and resolutions to common problems. Now, here’s how to here is how to disable the DNS lookup.

1. Connect your computer to the router by connecting a cable between the console and a terminal adapter that is joined to one of the PC’s serial communication ports like COM1, COM2 or COM3.

2. Start a terminal application like HyperTerminal. Configure the port setting relative to your program.

3. Now you should be in EXEC mode of the terminal server. Sometimes no prompt appears in which case you should press Enter a couple of times. Then type enable and hit enter again.

4. The default setting is for the DNS lookup to be enabled. Obviously, you are trying to disable it so you need to know the disable command. It is: Router(config) #no ip domain-lookup.

5. That’s it. If you wish to enable the DNS lookup again you will use the same command sans no. So it looks like this: Router(config) #ip domain-lookup.

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Disable on a Server

If you are trying to disable DNS lookups on a MySQL server, here’s how you do it.

1. Start up MySQL server software with the skip-name-resolve option.

2. DNS lookups are controlled by a command called “HostnameLookups” on the Apache server. This is probably set to on by default so all you need to do is change this to the off setting and the DNS lookup will be disabled.

3. To enable it, just use the directive “HostnameLookups” and switch it back to on.

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