DNS - Introduction

Introduction

Perhaps the most important, and occasionally most troublesome aspect of running a web site, is the issue of the Domain Name System [DNS]. DNS is the method through which a web site can be located, without knowing where it is physically located on the internet.

IP Addresses

In actuality, the true address of a web site is its Internet Protocol, or [IP] address. This is a numeric address that indicates where the computer is physically connected to the internet.

Example - IP addresses are numerical addresses - four numbers separated by dots: e.g.: 209.59.139.20

Your IP Address - When your account is activated, you will be notified of your site's IP address in the introductory email. - Make note of it!

This IP address is, for all intents and purposes, the permanent address of your site while it is hosted at PappaShop. Should your IP address need to be changed [e.g. if your site is moved to a different PappaShop server machine] you'll be notified at the time.

Your IP address is synonymous for your domain name. In most internet applications, the IP address can be used in place of the domain name - e.g. when configuring our email client, when asked for the mail server, you may enter the IP address instead of 'mail.yourdomain.com'

Starting Out - During the first few days or so after a new account activation, you will need to use your IP address instead of your domain name, as the DNS takes time correctly point to your PappaShop site.

DNS Servers

Domain names are much easier to remember than IP address, but they give no indication as to how to find the site on the internet. This is done by the DNS system, which resolves domain names into their 'real' address - the IP address.

When a web browser connects to 'www.yourdomain.com', a message is sent to your local DNS server [usually at you internet service provider if you are at home, dialed into the internet] which sends back the IP address of the domain. The browser uses this IP address to connect to the web server and receive the pages. This is called resolving the address.

Benefits - The benefits of the DNS system are apparent- domain names are easy to remember, and we can change where a domain name goes to by changing the IP address that the DNS servers point it to - a web site may move to a different computer halfway across the world, yet it will still be reachable by its domain name, so long as the DNS system is updated with the new IP address.

Synchronization - Problems arise with this system because of the issue of synchronization. Every ISP has its own DNS server - what if one ISP's DNS server points your domain to a different IP address than the other? People on different ISP's, looking for www.yourdomain.com could be sent to different sites, and may not be able to connect to your web site at all.

Master Servers - Clearly there must be a system to ensure than DNS servers everywhere have access to the same, consistent information about the IP addresses of web sites and internet domains. This is why we have the system of authoritative name servers and master servers.

Master DNS servers, the next part of the DNS system, are the thirteen master DNS servers that hold the 'top level' information for the entire internet's DNS system. These thirteen systems, operated by a gathering of private companies, academic institutions and military laboratories, have the job of propagating IP address information from each domain's authoritative DNS servers, to other DNS servers across the planet.

Authoritative DNS Servers: every domain must have two DNS servers to act as their Authority or Primary . These are the servers that hold the most correct and up to date information regarding the domain's IP addresses. Usually these DNS servers are operated by the owners of the domain in question [or their hosting provider, as is the case with PappaShop customers]. Other DNS servers across the internet will trust the authoritative name servers to provide the correct address for a host or domain on the net.

Example - Let's take a look at how your browser receives the IP address of a web site you wish to view: Here's a common example - www.microsoft.com

» You enter 'www.microsoft.com' in Your browser's address bar
» Your browser sends a message to your ISP's DNS server.
» The server looks in its records to see if it has the address for www.microsoft.com
» Seeing that it does not have the IP address for microsoft.com, it must ask the authorative name server for the address.
» Microsoft.com is part of the .com top-level domain [TLD], so it asks the .com TLD which name servers are authorative for microsoft.com.
» The ISP's name server then connects to those name servers, asking for the IP of www.microsoft.com and passes this address to your browser.
» The ISP's name server stores the address in it's cache until the time to live [TTL] has expired. This cuts down on traffic to the master name servers.

Domain Registrars

There is a piece missing from the system just described however. The master servers have a list of all known domains and their authoritative servers; but where does this list come from? how is it kept up to date? The answer is the Domain Registrar.

Every Top Level Domain, such as .com .org .net .edu has its own domain registrar; a beaurocratic body designated to maintain information about internet domains. These records include information about the owner of the domain name, contact information for the system administrator, and the addresses of authoritative name servers for the domain. These records do not contain the actual IP address of the domain, as this may change over time, and it is the job of the authoritative name server to provide current addresses for a domain.

There are currently several domain registrars which can service you. PappaShop Inc. uses Bulk Register. However you are welcome to use any domain registrar you choose if you feel that you do not want your domain registered through PappaShop Inc. Here is a list of Domain Registrars.

Other top-level Domains have their own Registrar authorities. In Europe, TLD's so such as .uk .de .no .ie .fr and other country code TLD's are operated by RIPE.

Domain Registrars register your ownership of a domain and its authoritative name servers, with the Master DNS servers, for a yearly fee. They also maintain the database of authoritative name servers for each domain in the TLD's they control.

Whois Records

This database is commonly called the WHOIS database, and parts of it are publicly accessible over the internet. It is named after the tool used to access the database over the internet.

There are several whois client applications available for all operating systems, but today the easiest method is to use a web-based whois query tool.

InterNIC -
http://www.internic.net/whois.html 
RIPE -
http://www.ripe.net/db/whois.html 

Domain Modification

PappaShop DNS Servers - The most common change you will have to make, is the alteration of your domain's name servers if you are transferring your domain from a previous hosting service. The fields you must adjust appear as follows, please see your welcome email for this information

Primary Server Hostname: 
Primary Server Netaddress:
Secondary Server Hostname:
Secondary Server Netaddress:

Troubleshooting DNS Problems

So there's a problem with your domain, what do you do? DNS problems can be some of the most thorny problems to resolve, essentially because there are many points of failure, only a few of which are under the control of PappaShop.

Points of Failure - There are essentially four main points of failure for the DNS system:

» PappaShop DNS Servers
» InterNIC [or the relevant registrar body for your domain] and your domain record itself
» The thirteen root DNS servers can provide DNS synchronization across the whole internet
» Your ISP's local DNS server

The best way to asure a rapid resolution to any domain related problem is to provide us with as much information about the problem as possible. Please see the Tools section for help on diagnosing DNS problems.

DNS Tools

The following DNS tools are invaluable for diagnosing DNS problems. You may wish to use these yourself, or at least be aware of their purpose so as to clarify information you receive from tech support about the DNS problem.

ping - A tool used to determine if a connection can be made to a remote domain or IP address over the internet from your computer. Ping sends out data to the remote machine and listens for replies indicating the serer can be reached from your location.


nslookup - Is short for 'name server lookup'. Nslookup queries a DNS server for the IP address of a given computer or domain. As noted earlier in this section, this is referred to as resolving the address. An important part of solving DNS problems is to query DNS servers in several important locations to determine which servers can successfully resolve your domain to its IP address. In this manner we can rapidly isolate the problem and provide a solution.


traceroute
- traceroute is something of a combination of the two previous tools. As the name suggests, it traces the route between your computer and a remote system, indicating the networks and computers your data passes through on the route to its destination.


whois - The client tool for the database system of the same name. A whois utility allows you to look up information on domain records. Most domain registries have whois tools built into their web sites now , so obtaining a separate whois tool is now largely unnecessary.


Checklist - Here's the checklist of information to obtain for resolving DNS problems. The more of these you can provide to us, the quicker we can provide a solution.

» Can you ping your web site by domain name? ping [your domain name]
» Can you ping your web site by ip address? ping [your ip address]
» Does your local DNS server resolve your domains to its correct IP address? nslookup [your domain name]`
» Does your Whois record indicate the correct DNS servers [i.e. ns1.pappapakX.com] in the name servers by order' section? whois [your domain name]
 

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