DNS is much like a phone book for the internet. For each domain name (or subdomain like ‘www’), there is an IP address that resembles a phone number. Getting the matching number for each domain can take some time and make your site appear slow, particularly on mobile connections. Fortunately, you can pre-request this information and speed up your site in most cases.
To enable a domains DNS lookup to be performed in advance of the request, you can add a single line to the
<head> section of your page.
<link rel="dns-prefetch" href="//giantgeek.com" />
If you want to explicitly turn on (or off) this behavior, you can add one of the following, or their HTTP Header equivalents:
<meta http-equiv="x-dns-prefetch-control" content="on" />
<meta http-equiv="x-dns-prefetch-control" content="off" />
This is supported in all modern browsers:
- Firefox 3.5+
- Safari 5.0+
- MSIE 9.0+
If should be noted that a similar method can be used to prefetch as page, but I will save that for a different article:
<link rel="prefetch" href="http://www.skotfred.com/" />
Categories: WebStandards, Work browser, cache, dns, fetch, head, header, html, http, link, lookup, meta, pre, rel, resolution, resolve
If you take a close look at your logs you may occasionally see requests for a file named
wpad.dat. This file is related to automatic proxy configuration in many browsers.
To provide this capability to your users and website,
Default behavior is to traverse the domain in reverse, looking for one with a file named
Example (using my domain for example):
- Then in httpd.conf, set the MIME type:
AddType application/x-ns-proxy-autoconfig .pac
- Also in httpd.conf, add a redirect to the actual file you wish to use.
Redirect permanent /wpad.dat http://www.giantgeek.com/proxy.pac
- In the new file, add the following default contents, modify if you use a proxy:
/* 'proxy.pac' - This is the main function called by any browser
NOTE: there is NO proxy!
function FindProxyForURL(url, host)
} // End function FindProxyForUrl
This is a concept I had forgotten about until recently, it can often serve as a simple means of code obfuscation and is also sometimes referred to as “Decimal Address”.
- DNS is used to convert a URL/domain name into an IP address that is used to contact the remote machine.
localhost = 127.0.0.7
giantgeek.com = 22.214.171.124
- IP addresses (as IPv4) are represented as groups of 4 hexadecimal or decimal octets.
- Those numbers can be plugged into a simple formula to be represented as a single large integer.
As such, you can use the following as equivalents:
Since I’ve run a few small websites (like this one) out of my home for years, I’ve found it useful to run a DNS server inside of my firewall. Not only does this make it easier to maintain the websites, but it allows me to lock down security and increase performance of many of my applications.
I run a the following services that use DNS:
- Apache JAMES – mail server that does lookups to send email and filter inbound SPAM.
- Analog – web server log analysis.
- Apache HTTPD – web server, used to host websites, private domains used for internal purposes.
To make things more efficient, I currently have my DNS setup to forward all requests to OpenDNS, allowing for ‘adult’ website filters and analysis of DNS activity.
Some open-source/free DNS servers that I recommend:
I’ve used EveryDNS (free service) for years to host my DNS services. Recently I found that they now offer public DNS service for lookups as OpenDNS. While I still run my own private DNS server for caching and various private addresses. I now do a simple forward lookup to their servers to gain the extra services they provide… notably Phishing and typo protection.
Setup is very simple for most users, and even a non-technical person should have no problems following their installation instructions for a single computer/device or an entire network.