The fqdn of a name server that has authority over a domain is noted in what type of dns record?

If we had to remember the IP addresses of all our favorite websites, we'd probably go nuts! Human beings are just not that good at remembering strings of numbers. We are good at remembering words, however, and that is where domain names come in. You probably have hundreds of domain names stored in your head, such as:

• howstuffworks.com — our favorite domain name
• google.com — one of the most used domain names in the world
• mit.edu — a popular EDU name
• bbc.co.uk — a three-part domain name using the country code UK

You'll recognize domain names as having strings of characters separated by dots (periods). The last word in a domain name represents a top-level domain. These top-level domains are controlled by the IANA in what's called the Root Zone Database, which we'll examine more closely later. There are more than 1,000 top-level domains, and here are some of the most common:

• COM — commercial websites, though open to everyone
• NET — network websites, though open to everyone
• ORG — non-profit organization websites, though open to everyone
• EDU — restricted to schools and educational organizations
• MIL — restricted to the U.S. military
• GOV — restricted to the U.S. government
• US, UK, RU and other two-letter country codes — each is assigned to a domain name authority in the respective country

In a domain name, each word and dot combination you add before a top-level domain indicates a level in the domain structure. Each level refers to a server or a group of servers that manage that domain level. For example, "howstuffworks" in our domain name is a second-level domain off the COM top-level domain. An organization may have a hierarchy of sub-domains further organizing its internet presence, like "bbc.co.uk" which is the BBC's domain under CO, an additional level created by the domain name authority responsible for the U.K. country code.

The left-most word in the domain name, such as www or mail, is a host name. It specifies the name of a specific machine (with a specific IP address) in a domain, typically dedicated to a specific purpose. A given domain can potentially contain millions of host names as long as they're all unique to that domain. (The "http" part stands for Hypertext Transfer Protocol and is the protocol by which information is sent by the user to the website she is visiting. Nowadays, you're more likely to see "https" which is a sign the information is being sent by secure protocol where the information is encrypted. This is especially important if you're providing a credit card number to a website [source: EasyNews].)

Because all of the names in a given domain need to be unique, there has to be some way to control the list and makes sure no duplicates arise. That's where registrars come in. A registrar is an authority that can assign domain names directly under one or more top-level domains and register them with InterNIC, a service of ICANN, which enforces uniqueness of domain names across the internet. Each domain registration becomes part of a central domain registration database known as the whois database. Network Solutions, Inc. (NSI) was one of the first registrars, and today companies like GoDaddy.com offer domain registration in addition to many other website and domain management services. [source: InterNIC]

Later, when we look at how to create a domain name, we'll see that part of registering a domain requires identifying one or more name servers (DNS servers) that have the authority to resolve the host names and sub-domains in that domain. Typically, you would do this through a hosting service, which has its own DNS servers. Next, we'll look at how these DNS servers manage your domain, and how DNS servers across the internet work together to ensure traffic is routed properly between IP addresses.

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DNS stands for Domain Name System (DNS) services. When we access a website, we are using this service to locate the server where the domain's website is located. When browsing the web, we usually type in a domain name like www.google.com into our browser. This is better than trying to remember an IP address linked to a Google server.

Behind the scenes, a conversion happens using this service which converts www.google.com to 172.217.12.46. The IP address designates the location of a server on the Internet. This conversion process is called a query. This is an integral part of how devices connect with each other to communicate over the internet. To understand the query process, let’s review how this query works.

Let's visit a website by typing a domain name into a web browser. Our computer will start resolving the hostname, such as www.liquidweb.com. Our computer will then look for the IP address associated with the domain name in its local DNS cache. This cache stores this information that our computer has recently saved.  If it is present locally, then the website will be displayed. If our computer does not have the information, it will perform a DNS query to retrieve the correct information.

If the information is not in your computer’s local cache, then it will query another server. Recursive DNS servers have their local cache, much like your computer. Many ISP’s use the same recursive DNS servers, it's possible that common domain name is already in its cache. If the domain is cached, the query will end here and the website displayed to the user.

If a recursive DNS server or servers do not have information stored in its cache memory, it looks elsewhere. The query then continues up the chain of authoritative DNS servers. The search will continue until it finds a nameserver for the domain. These authoritative name servers are responsible for storing these records for their respective domain names.

To locate the IP address for liquidweb.com, we will query the authoritative name server for the address record (A record). A Recursive DNS server accesses the A record for liquidweb.com from the authoritative name servers. It then stores the record in its local cache. If another query requests the A record for liquidweb.com, the recursive server will have the answer. All DNS records have a time-to-live value, which shows when a record will expire. After some time has passed, the recursive DNS server will ask for an updated copy of the records.

The Recursive DNS server has the information and returns the A record to your computer. Our computer then stores the record in its local cache. It reads the IP address from the DNS record and passed it to our browser. The web browser will connect to the web server associated with the A records IP and display the website.

The entire lookup process, from start to finish, takes only milliseconds to complete. For a better understanding, let’s break down the components that make up the lookup process.

An authoritative name server is a server that stores DNS records (A, CNAME, MX, TXT, etc.) for domain names. These servers will only respond to queries for locally stored DNS zone files.  Say a server in our network has stored an A record for example.com. That server is the authoritative server for the example.com domain name.

A recursive name server is a DNS server that receives queries for informational purposes. These types of servers do not store DNS records. When a query is received, it will search the cache memory for an address linked to the IP address. If the recursive name server has the information, then it will return a response to query sender. If it does not have the record, then the query will be sent to other recursive name servers. This continues until it reaches an authoritative DNS server that can supply the IP address.

A DNS zone is an administrative space within the Domain Name System. A zone forms one part of the DNS namespace delegated to administrators or specific entities. Each zone contains the resource records for all of its domain names.

A DNS zone file is a text file stored on a server. It contains all the records for every domain within that zone. It is mandatory for the zone file to have the TTL (Time to Live) listed before any other information. The TTL specifies how long a DNS record is in the server’s cache memory. The zone file can only list one record per line. It will display the Start of Authority (SOA) record listed first. The SOA record contains essential domain name information including the primary authoritative name server for the DNS Zone.

DNS records are stored in authoritative servers. These records provide information about a domain, including its associated IP address for each domain. It is mandatory for all domains to have a specific set of default records. Below are a list of the most common record types and frequently utilized DNS records. Let’s look over each type of record.

CNAME (Canonical Name) Record

SOA (Start of Authority) Record

Now that we have reviewed the DNS services and components, we can begin troubleshoot DNS issues which can arise. Below is a list of common DNS troubleshooting tips.

Although DNS can be a complex issue, a better understanding of the process is always helpful. These troubleshooting tips can prepare us to work with DNS. The following tools are quite useful when checking DNS propagation or records.

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