Domain Name System (DNS) tweaks

Posted on December 24th, 2008 by Richard Catto 1,734 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
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Firefox add-on Search Cloudlet for Google and Yahoo

Posted on December 20th, 2008 by Richard Catto 2,069 views

This is a truly innovative add-on for the Firefox web browser, that is causing me to rethink my use of Google Chrome as my browser of choice.

Currently Google Chrome does not support add-ons, but apparently will in the future.

With the Search Cloudlet add-on, when you search with either Google or Yahoo, you will get a tag cloud generated which summarises your search results into a tag cloud. The tag cloud comprises all the keywords relevant to your search term. Clicking a tag, adds it to your search terms and refreshes the search with results which zero in on what you want.

You can also see which sites are represented in the search results.

This add-on was written by a research organisation - The International Software and Productivity Engineering Institute (INTSPEI).

Tags: Firefox, Google, INTSPEI, search, yahoo
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The WebCredibles!

Posted on August 23rd, 2008 by Richard Catto 1,697 views

The usual suspects

This is a great little Webcomic devoted to informing web designers on the concepts of usability and accessiblity!

Tags: accessibility, usability, Webcredibles
Filed under Cartoon, Web design | No Comments »

Losing Firefox 3 web browser cookies?

Posted on July 22nd, 2008 by Richard Catto 7,195 views

Problem

Whenever you close your Firefox 3 web browser, it manages to lose all your cookies so that the next time you start it up, you have to re-login to all your favourite sites.

This might occur after a forced restart of your Windows Operating System.

Cause

A corrupted cookies.sqlite file

Resolution

Delete the cookies.sqlite file. Close Firefox before attempting to do this.

On Windows, this file may be found here:

C:\Documents and Settings\[Username]\Application Data\Mozilla\Firefox\Profiles\[ProfileID]

The next time you open Firefox 3 web browser, your cookies.sqlite file will be re-created and your login cookies will be correctly stored. You can now close your browser and the next time you open it, you will remain logged in to all your favourite sites.

Tags: cookie loss, Firefox 3 web browser
Filed under Firefox web browser | 14 Comments »

How to check whether a site is up or down

Posted on July 8th, 2008 by Richard Catto 1,325 views

This is a common problem that afflicts anyone who uses the Internet. Sometimes you type in a url to a site you use often and find you can’t get it to load. So then you wonder where the fault lies. Is the site really down or has something gone wrong with your ISP or perhaps even your own connection to the Internet?

Well someone, Alex Payne to be precise, decided to create a web site to answer that very question.

It’s called Down for everyone or just me?

You just type in the url you want to access and hit enter and it’ll tell you whether or not it can access the site or not.

That gives you some valuable information to help you decide where the problem lies. The Down for everyone site is itself hosted on Google’s servers, so obviously if Google is down, it will be too.

Ironically, Alex Payne works for twitter which often experiences down time, which is perhaps what gave him the impetus to create this online web service in the first place.

You can read more about this over on the New York Times.

Tags: Alex Payne, online
Filed under Web service | 1 Comment »