DNS lookup describes the process of querying a record from a domain name system server. The DNS record can be used to find IP addresses for a specific domain name and vice versa, and to find out more information. There are various programs and online tools for performing lookups.
The process gives people, computers, or applications the IPv4 or IPv6 address that is necessary to communicate with a specific computer over an IP network. In its data packets, the Internet Protocol only addresses IP addresses and no domain names. However, since users can remember speaking domain names more easily than the relatively cryptic IP addresses, they prefer to access systems with domain names, for example, via the address line of the browser.
You may want to read related guidelines to have more information:
Forward and Reverse DNS-Lookup
The process of resolving an IP address to a given domain name is known as a forward DNS lookup or simply as a DNS lookup. The reverse process is called reverse DNS lookup, inverse DNS lookup, or just IP lookup. For a reverse DNS lookup, it is first necessary to formally convert the IP address into a name. Since IP addresses and domain names have different directions in which the data become more specific, the IP address is reversed in a second step in the same order. This name is used to request the PTR resource record from the Domain Name System.
Result Content of a Lookup
However, a domain name system can provide much more information than just the assignment of IP addresses and domain names or vice versa. For example, the response from a DNS server contains the TTL field (Time To Live). It provides information about how long the entry is valid and how long the data should be kept in its own cache. An A record provides the IPv4 address associated with a domain name, an AAAA record the corresponding IPv6 address. The PTR record contains the domain name for an IPv4 or IPv6 address. The entry MX-Record provides information about which server accepts emails for a specific domain name. The managing name servers of a domain are listed in the NS record. Other content can be:
- the SOA record
- the LOC record
- the TXT record
DNS Lookup Usage Example
In order to clarify the process of a lookup, a brief application example follows. Suppose a browser wants to connect to an “xyz-server.de” web server. For this, he needs the server’s IP address. The computer first checks locally whether the name entered is in its cache or in its hosts’ file. If this is not the case, he asks the responsible server. This was assigned to it via DHCP or is configured permanently.
If the server can answer the request itself, it delivers the answer to the requester. If not, he contacts another server responsible for the domain. With the supplied IP address, the browser can communicate with the webserver via the IP network (Internet).
Another example of the use of DNS lookup is the checking and filtering of mails by an email server. DNS lookup, reverse DNS lookup, and the HELO hostname of the SMTP protocol must match and correspond to the sender.
Perform Lookups Manually Using the Nslookup Command from a Computer
The DNS lookup can be carried out manually using a command from a computer. For this purpose, the “nslookup” command is used in operating systems such as Linux, Windows, or macOS. The command supports forward and reverse DNS lookup and has numerous options. It can be executed from the command line interface of a computer.
Web tools for DNS lookup
There are numerous web tools for DNS lookup on the Internet. Whois.com provides one of these tools. It can resolve browser-based domain names and provides information from the A, AAAA, CNAME, MX, NS, SOA, or TXT records. Simply enter a publicly known domain name in the query box of the web interface.
Relevance of DNS servers for SEO and online marketing
The resolution of an IP address always takes some time and has an impact on the loading time of a website. This process is usually completed in a fraction of a second. However, if there is a delay, this will result in longer loading time and thus often higher bounce rates, as the user experience is impaired. Since the bounce rate is an important ranking criterion, the ranking of a website can be negatively influenced. To prevent this, webmasters can use the Google Search Console to detect possible name resolution errors and, if necessary, take suitable measures to rectify them.
Also, checking the IP Addresses with DNS Reverse Lookup for backlink and off-page profile of a web site is important. With DNS Look Up, checking the server speed is also possible. As Holistic SEOs, we will continue to search about DNS and IP Addresses for better Search Engine Optimization processes.