What is DNS?
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 126.96.36.199. 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.
How Does the DNS Process Work?
Step 1: Requesting Website Information
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.
Step 2: Contact the Recursive DNS Servers
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.
Step 3: Query the Authoritative DNS Servers
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.
Step 4: Access the DNS Record
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.
Step 5: Final DNS Step
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.
Authoritative DNS Server
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.
DNS Zone File
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 Record Types
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.
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.
- If our website displays "Server IP address could not be found," it's possible that the A record is missing. You will need to add an A record to your DNS zone.
- Check to see if you have any improperly configured DNS records.
- When you change your name servers, we need to wait for the name servers to propagate. The propagation can take 24 - 48 hours to complete propagate across the internet.
- Check to see if you have high TTL (Time to Live) values. If an A record has a default TTL value of 86400 seconds (24 hours). If we update the an A record, propagation will take 24 to 48 hours to disperse. It is better to change the TTL value to 300 seconds which is 5 minutes. We have a great article that talks more about TTL values.
- If we use a third-party proxy server and our website is not displaying. We can use our local host file to see where the issue is occurring. Our website is called dnswebtest.com. This domain is using a third-party proxy server. If there's a connection error, we can usually locate where the error originates. To locate the issue with the host or the proxy server, we investigate. To troubleshoot, we will modify our local host file. We add the website dnswebtest.com as an entry to the host file. Then, point it to the web hosting company’s IP address, for example, 188.8.131.52. If we visit the website and it displays correctly, we know the issue is with the third-party proxy server. Here is an excellent article on How to Edit Your Host File.
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.
- https://www.whatsmydns.net/ for DNS propagation
- https://www.whoishostingthis.com/ to show what IP address a website is resolving to
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