Domain Name System (DNS) tweaks

Posted on December 24th, 2008 by Richard Catto 1,053 views

The Domain Name System has been the way we use the Internet since 1983. The underlying protocol of the Internet, TCP/IP, identifies each device attached to the Internet by one or more IP addresses which are difficult for people to remember and do not describe the nature of the device.

DNS assigns a hierarchical name to each device. Prior to DNS, a central HOSTS.TXT file was used which listed all the devices attached to the Internet. Whilst the Internet comprised a small set of devices, this system sufficed but it does not scale beyond a few thousand devices. After that the database simply becomes too massive.

The DNS system allows a name to be attached to IP addresses, so that one can type in a domain name instead of a dotted quad IP address (IPv4).

An ISP or web hoster usually supplies their subscribers with at least two IP addresses which represent the nameservers you use to do DNS lookups. However, not all nameservers are created equal. Some are faster than others, some are more accurate (because they update their caches more frequently).

Since July 2006, a totally free DNS service has been available for anyone connected to the Internet to use in lieu of the ones their ISP or web hoster gives to them. It’s called OpenDNS and it offers much more than simply domain name resolution (the process of translating a hostname into an IP address).

OpenDNS also allows subscribers to filter out harmful sites and sites not suitable for minors. To use OpenDNS, simply substitute the IP addresses of their publicly accessible name servers for those supplied to you by your ISP. Instructions for setting up PCs and routers are available on their site. You may also create an account with them which allows you access to more advanced features and stats.

For people with dynamic IPs, which includes most people connecting to the Internet via an ISP, OpenDNS has a utility, OpenDNS updater, which will automatically update your OpenDNS account with your new IP address whenever you are assigned a new one. This allows you to track your stats and keep your settings across multiple IP addresses.

OpenDNS is fast, accurate and reliable. It definitely enhances one’s Internet experience. However, there is another issue to look at too.

Since Windows 2000, Windows also runs a local DNS cache on your PC which by default takes too long to refresh itself, because it’s TTL (Time To Live) value is set to 24 hours, which means that if a site gets a new IP address, you will not be able to resolve it’s new value until your local Windows DNS cache has expired.

Windows provides a way of shortening the TTL by setting new values in registry parameters. You can add these parameters in yourself using the built in Windows tool, regedit.

Instructions on what parameters to change and how are provided in this Windows Help and Support page:
How to Disable Client-Side DNS Caching in Windows XP and Windows Server 2003 

I set my TTL value to 4 hours for postive responses and to 0 hours for negative responses and I can tell you it made a difference. If you are registering new domains or transferring them between servers, you definitely want to change your default TTL values or you will be frustrated to discover that while the IP address changes have propagated to most people, your local Windows DNS cache still retains the old values.

Tags: DNS, OpenDNS, TTL
Filed under Internet |

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