DNS Tutorial
DNS Tutorial by Scott Meyer
This is a tutorial to explain DNS, what it does, and how it relates
to your website. For purposes of the tutorial, we shall assume that
the user is a home user connected to a ISP with dial-up, cable,
DSL, etc. The same ideas apply to businesses, but things can get
complicated quickly depending on how the business is set up. Dealing
with those complications is beyond the scope of this tutorial.
Before we get into DNS, lets start off with breaking down a web
address. This is also known as URL or Uniform Resource Locater.
It essentially gives where the web page is, and how you need to
talk to it. Lets use the example of:
http://www.onlyonecreations.com/pages/wood-gift-pen.htm
The first part is "http://", and that tells your PC what protocol
(what language so to speak) to use talking with this site. In this
case, you are using HTTP (HyperText Transfer Protocol). Another
very common one for web designers to use is "ftp://" or File Transfer
Protocol. You would use it to connect to your webserver to put the
web pages you created onto the server.
You also see "https://" quite commonly. This simply means that
you the connection between you and the web server is secure (meaning
the information being sent back and forth is encrypted). You should
see "https://" when you (or your customers) are checking out, especially
when they are entering credit card information.
The next part, "onlyonecreations.com" is called the domain name.
The "www" used to be more significant than it is today. Today, the
"www" is, for the most part, assumed and you can get to the same
page regardless of whether or not you type in "www" your browser.
The part "/pages/wood-gift-pen.htm" tells the web server to look
in the directory called "pages" and send the file called "wood-gift-pen.htm"
to your browser. It is just like the directories on your PC.
Before we get into DNS, we need to explain what an IP address is.
Every PC and server has an IP address on the Internet. It has the
format of 4 numbers, separated by periods, and looks like "64.17.143.84".
Each number should be between 0 and 255.
Think of it as your phone number on the internet, it must be
unique. It would be bad to have 2 different houses with the same
phone number, and it would be bad to have 2 different machines (more
properly known as hosts) that have the same IP address on the Internet.
For most people, it is much easier to remember "www.onlyonecreations.com"
than it is to remember "64.17.143.84". When you enter a URL into
your browser, you usually use the easy to remember name.
How does your PC know where to find "www.onlyonecreations? Remember
that each machine has a IP address? There is a way to translate
from the easy to remember domain name, and the hard to remember
IP address.
Enter DNS. DNS is an acronym for "Domain Name Service". It's whole
purpose in life is to translate between the friendly "www.onlyonecreations.com"
and the not-so-friendly 64.17.143.84. It handles this translation
for web sites, email, FTP servers, database servers, or any machine
within a domain name.
Let's dig into the process of how that works. Let's use the example
that Scott types "www.onlyonecreations.com" into his web browser.
How does his PC find the web server that has the page he's looking
for, among the thousands of web servers?
-
Scott types in www.onlyonecreations.com to his browser.
-
Scott's PC looks at it's configuration. It will find something
called "DNS Server" or "name server" and there will be an IP address
associated with that. Let's say it is 198.6.1.1. Scott's PC sends
a message to 198.6.1.1 and asks "I am looking for the IP address
of www.onlyonecreations.com, can you tell me what it is?"
-
The DNS Server (198.6.1.1) gets the message, and assuming that
the server already knows what the IP address of www.onlyonecreations.com
is, it tells Scott's PC that the IP address is 64.17.143.84. I
will get into considerable more depth about the DNS server, how
it works, and why it is important to a web site owner, a little
later.
-
Scott's PC gets the message that the IP address of www.onlyonecreations.com
is 64.17.143.84. So his PC sends a message to 64.17.143.84 and
asks "send me the default web page at 64.17.143.84".
-
The web server (whose IP address is 64.17.143.84) sends the
web page to your browser. That is a simplistic example of how
your PC finds a particular web-server and web page. The process
of matching a domain name to a IP address is called resolving.
So your PC resolves the IP address from the domain name. Let's
get into a little more detail.
For step 1, how does Scott's PC know that the IP address of the
DNS Server is? There are 2 ways it learns what the address is. The
first is that Scott asked his ISP what the address was, and entered
it himself. There are times manually entering (also known as statically
entering) the address is necessary or desirable, but usually the
ISP automatically tells your PC what the IP address of the DNS server
is.
This process is called "DHCP" or Dynamic Host Configuration Protocol.
When you select "Obtain IP address automatically" in your windows
Network connections page, you are telling your PC to use DHCP and
to ask the ISP to give you the DNS Server address (among a bunch
of other things).
In step 3, we assumed that the DNS server already knew what the
IP address of www.onlyonecreations.com was.
What if it didn't already know?
Let's assume that the DNS server Scott's PC sent a request to,
doesn't know where www.onlyonecreations.com is.
Have you ever noticed that there are only so many variations of
the end of the domain name? There are .com, .gov, .net, .org, .us,
.biz, among others. When a DNS server receives a request to resolve
an IP address (translate from a domain name to a IP address) for
a domain that it doesn't know the answer to, it sends a message
to any one of a small number of servers. That small number of servers
are responsible for knowing what the "authoritative server" is for
EVERY domain name. A realm would be .com, or .org for example, and
is properly called a top-level domain.
What is an authoritative server? An authoritative server is a DNS
server that has a Statement of Authority configured for a particular
domain name. That means that the server has absolute and total knowledge
of the domain, any information that contradicts the information
that the server has is wrong, it is the final word.
This becomes more important a little later. For purposes of this
discussion, let's ignore backup authoritative servers.
The message that Scott's DNS server sends to the top-level domain
server "what is the authoritative server for onlyonecreations.com?".
It is important to understand, that Scott's DNS Server is NOT asking
"what is the IP address of the web server for onlyonecreations?".
It is only asking "where do I go to find out where the web server
for onlyonecreations.com is?"
Once Scott's DNS server knows where to go to get the answer for
Scott's request, it sends a message to the authoritative server
asking "what is the IP address of the web server for onlyonecreations.com?".
The authoritative server responds, and Scott's DNS Server tells
Scott's PC the IP address it needs to connect Scott to the webpage
he is looking for.
To summarize the past few paragraphs, Scott's DNS server receives
a request for an IP address that it doesn't know. That server makes
a request of a top-level domain server, and gets a response with
where to go to get the information that Scott is requesting. The
DNS server then makes a request of the authoritative server, and
forwards the answer it receives to the PC that made the first request.
It sounds long and complex, but it happens very quickly. One
way to speed up the process is called caching. Caching is where
the DNS server remembers the response from the authoritative server
for a period of time. So if Bob makes the same request 5 minutes
after Scott did, the DNS server doesn't have to repeat the whole
process. Caching will be brought up again in a bit.
So we learned how your PC finds out where it needs to go to get
to specific web page. So what. What does that have to do with web
site owners? Let's explore.
You're a web site owner, you just got your site made (or had it
made). Now you want to register a domain name. What does that mean?
When you register a domain name, you need to talk to a "registrar".
You tell the registrar some information about you, and they ask
for a "name server", or "DNS Server" when you register the domain.
The exact term used will vary, but they all means the same thing
- what are the IP addresses for the authoritative servers for your
domain? These would generally be the DNS servers of your web host.
They will ask for at least 2, sometimes up to 4, but 2 are all that
are absolutely needed. Those after the first are used if the first
one is down.
For the sake of simplicity, that registrar is responsible for
telling the top-level domain servers the answer to the question
that Scott's DNS server asked "what is the authoritative server
for onlyonecreations.com?".
There are numerous companies that register domain names, and many
web designers and web hosting companies have a process to help make
this easy for you. However it gets accomplished, make SURE that
YOU own the domain name, not the web hosting company, not the web
site designer.
This is not as much of a problem as it once was. Many times in
the past, your web host/ISP/designer would own the domain name.
If you were unhappy with them for whatever reason, you could not
move your site to someone else without their blessing. They permitted
you to use the domain name because you were a customer. They locked
you in as a customer because it was very costly to change domain
name. It's essentially changing the name of your business, your
identity on the internet. They could also charge you whatever fee
they decided on to transfer the domain name to someone else, and
there was no guarantee they were willing to do that.
Again, not nearly as big a problem as it once was, but still
something to make sure you get ownership of.
Now you are thinking, that is a really long explanation for 2 paragraphs
of needed information. :) What happens if you picked a web host
that is the worst company on the face of the planet, or you have
outgrown what the web host is capable of providing, or maybe even
you decide to host your own website.
The first thing you need to do is plan. The basic process would
be that you sign up with a new web host, put a copy of your site
on the new web host, and make sure everything is working, sometimes
there will be glitches. Once everything is working, then you have
the registrar tell the top-level domain servers that the new authoritative
servers are at the new web host. So from then on, whenever Scott
wants to see your webpage, his DNS server is told by the top-level
domain server that the authoritative server is at the new web host,
and they in turn point to your new web page.
Now, I said to plan. There is a reason for that besides just making
sure everything works. Remember when I said that "caching" would
come up again? Now is that time. Remember that Scott's DNS server
cached the address for the web server of:
www.onlyonecreations.com,
meaning that it remembers that www.onlyonecreations.com is has
the IP address of 64.17.143.84. Most DNS servers are set to remember
that information for 24 hours. So if Scott requests your web page
at noon on Monday, Scott's DNS server will cache the IP address
of your web server until noon on Tuesday. If you change hosts at
1pm on Monday, Scott will get your old website until at least noon
on Tuesday. His DNS server is giving Scott's PC the information
it remembers, it doesn't check to see if that is still accurate.
So if your old website is down (maybe your shopping cart won't work
now that you have moved hosts, for example), Scott can't get to
your new website, until his DNS server refreshes the information
(which will point to the new web site).
Plan on a timeframe of 24-48 hours from the time your registrar
makes the change in the top-level domain server, before that change
is spread through the Internet. So what does this mean for your
planning? If your site is generally used by businesses, your site
won't be very busy over the weekend. Therefore, plan on making the
change on a Friday evening, by the time Monday rolls around, all
the DNS server caches have been cleaned out (timed out actually),
the DNS servers will have to ask the top-level domain servers, and
your new website well be accessible.
One word of caution, before you make plans, find out when you
need to tell the registrar when to make the change. It usually takes
a period of time, that you need to plan for. There is little you
can do about the 24-48 hour period.
As that time period elapses, more and more of the DNS servers
around the world with have their cache time out, and get the new
information pointing to your new site, hence fewer and fewer people
will be unable to access your new site. It generally is pretty manageable,
if you plan accordingly.
So we know what DNS is, what it does for us, and a basic idea of
how it works. We know what a registrar does, and why we need them,
and what an authoritative server does for us. We know why some people
may not be able to access our new site 5 minutes after we changed
hosts.
A customer just called and said my site is down. I call my web host,
and they say it's up. I call the customer and they still can't get
on. Now what? Time for some basic troubleshooting. I'm not going
to go into great detail, but enough for you to confirm things have
been done correctly, and figure out if the site is really down or
if there is something making it look like it is down.
Two of the best sites I have found for troubleshooting are:
There are a TON of tools here to help you figure out what the
problem is.
A few quick steps:
-
Can you get to other web sites? Including ones you have not
been to recently?
-
Can your customer access other sites?
One of the first steps you should take in troubleshooting your
site being down - type in the IP address of your web server in your
browser. If you normally type in http://www.onlyonecreations.com/pages/wood-gift-pen.htm,
type in http://64.17.143.84/pages/wood-gift-pen.htm. Does it work?
When you use the domain name, does it still not work? If you can
get to your site using the IP address, but not using the domain
name, the problem is DNS, it is not your web server.
Let's use some tools at www.dnsstuff.com to confirm some things.
The 3rd tool down on the left side is WHOIS lookup. Type in your
domain name there (example, "onlyonecreations.com"). That brings
up a page with 2 important pieces of information. One being who
owns the domain name (this should be your name and address for your
domain name). The other being the authoritative servers (called
domain servers here)- remember Scott's DNS server asking for the
authoritative server for onlyonecreations.com? These are the addresses
that the top-level domain servers answer with.
The top tool on the right is called DNS Lookup. Type in www.onlyonecreations.com,
make sure that A is selected, and click look up. There are some
interesting and useful pieces of information here. When I entered
my domain name, I got:
- Searching for A record for www.onlyonecreations.com at g.root-servers.net:
- Got referral to M.GTLD-SERVERS.NET. [took 197 ms]
- Searching for A record for www.onlyonecreations.com at M.GTLD-SERVERS.NET.:
- Got referral to ns1.ixwebhosting.com. [took 249 ms]
- Searching for A record for www.onlyonecreations.com at ns1.ixwebhosting.com.:
- Reports www.onlyonecreations.com. [took 100 ms]
Do you see "g.root-servers.net" and "M.GTLD-SERVERS.NET"? Those
are top-level domain servers. On the 2nd line, it says "got referral
to ns1.ixwebhosting.com". That should be the one of the domain servers
you saw in the WHOIS lookup a minute ago. The DNS server is being
told where to get the IP address of www.onlyonecreations.com (ie,
ns1.ixwebhosting.com). The next block of information tells you the
answer that the authoritative server gave to the question "what
is the IP address of www.onlyonecreations.com?". It says that www.onlyonecreations.com
has an IP address of onlyonecreations.com. What!? That's not an
IP address. Remember way back at the beginning, I mentioned that
you usually get the same page regardless of whether you type in
www or not? Here's why! Now click, back and remove the "www." from
the front of the domain name in the box, and click look up. Now
we see that onlyonecreations.com points to 64.17.143.84. www.onlyonecreations.com
points to onlyonecreations.com, which points to 64.17.143.84, so
it doesn't matter if someone types the www or not (in this case).
So now you can walk through and ensure that the servers that are
supposed to have to correct answers, do in fact have the right answers.
But how do I tell if my (or my customer's) DNS server is giving
me the right information? Click here : http://www.kloth.net/services/nslookup.php.
There are 3 boxes to be concerned with. The first one (called simply
Domain here) is the domain name (like www.onlyonecreations.com)
of the machine you are having problems getting to. The next box
(called Server here) is the DNS server you want to ask. The 3rd
box (called Query) is the type of record you are looking up. For
our purposes you want to look "A" (which is a regular type of name
or record) or "MX" (which is an email record - ie "where do I send
mail to at onlyonecreations.com?").
So to find what MCI's DNS Server (as an example) has for the
IP address of onlyonecreations.com, enter "onlyonecreations.com"
in the 1st box, 198.6.1.1 (MCI's DNS server) in the 2nd, and select
"A" in the third box.
Last thing, sub-domains. A subdomain can be used, for example, if
you have both wholesale and retail for your business. You could
have the retail part of your business as www.yourdomain.com, and
the wholesale as wholesale.yourdomain.com. Details are beyond the
scope of this tutorial, but the same general rules apply to subdomains
as it does to domains.
I hope this clears up confusion, and doesn't muddy the waters too
much.
Thanks,
Scott Meyer
www.onlyonecreations.com
We designed this banner using Xara Webstyle
4
Sometimes a program is so incredible that we
have to share it with others! We are extremely impressed with this
all new version of
Xara Webstyle 4 and are currently using it as a tool in
designing our sites! This is a "must have" tool for web designers!
Take a look at our complete
Xara Webstyle 4 Review today!
Try Xara Webstyle 4 FREE Today!
GNC Web Creations - 133 Depot Street - Post Office Box 8 - Water Valley, MS 38965 - (662) 473-0063
Copyright © 2003 - 2008 J. Walker of GNC Web Creations All Rights Reserved
|
