Computers connected to the Internet have no names; instead, they use hard-to-remember IP addresses (numeric address like 123.123.123.123). The Domain Name System (DNS) makes things easier for humans. It translates more readily memorized domain names to IP addresses needed for the purpose of locating servers.
DNS servers are servers running special software. Originally, they stored only DNS tables containing domain names with corresponding IP addresses, the so-called A records. For example:
Domain Server's IP address
nic.ru 115.115.115.115
Today the DNS also contains other types of resource records: MX, TXT, CNAME, etc. They are required to enable the domain's use as a website address, mail exchange, and other services.
Resource records are DNS records containing names and corresponding information about servers to which such names must point. Each resource record is required for a specific service. For instance, MX stands for Mail eXchange. MX records are required to ensure email delivery.
You can't use a website or email with your domain without storing information about your domain on DNS servers. To ensure fail-safety, DNS servers are used in pairs: if one of them fails, it won't affect the website's availability.
Dynamic DNS provides a persistent addressing method for devices (computers, routers, webcams) with dynamic external IP addresses.
This service is intended for assigning a good-looking and easy-to-remember permanent domain name to your networking device (such as a router), so that this name will not depend on what kind of IP address is used (dynamic or static). Hostname with dynamic DNS will be mapped to your dynamic IP address. When IP address is changed, dynamic DNS client will send a notification to the servers of the DNS-hosting service with a current IP address, and the changes will be propagated throughout the Internet in a matter of seconds.
Dynamic DNS is supported on all plans of the DNS-master service. To configure dynamic DNS, you need to get a username and a password in the section Manage your account → DNS-hosting: Dynamic DNS". This login information may be used for configuration of dynamic DNS for all the DNS-hosting services.
After a new request, previously generated username and password will become invalid. You will have to reconfigure dynamic DNS with new login information. Instructions for developers are available on a special page.