A DNS resolver is a computer dedicated to the name resolution service on a network. Its primary function is to resolve names with IP addresses. In other words, a resolver computer is a computer that resolves names with IP addresses on the network at the fastest possible speed. This can be a DNS server or a system configured to communicate with DNS servers to resolve IP addresses.
Characteristics/functions of a DNS resolver system
A resolver system has several characteristics and functions that make it an important part of a network:
It removes the burden of managing records in the hosts file from other computers.
It reduces the number of DNS servers' IP addresses you need to configure on each network system.
It improves the network's performance and efficiency.
It maintains a list of all available DNS servers and sends queries to them in sequence until it gets an authoritative answer for each query.
How does a DNS resolver system work?
A resolver system can work in two ways depending on whether it is a DNS server or not:
If the resolver system is a DNS server, it checks its database, finds the IP address associated with the name and sends the reply message back to the system which sent the query message.
If the resolver system is not a DNS server, then it works as a mediator between the local system and DNS servers. It receives queries from the local system and forwards that query to all configured DNS servers in a sequence until it gets the IP address of the name it is looking for.
Once it gets the IP address associated with the name, it does not send the query to the next DNS server for that name. Usually, resolver systems are also configured to cache the result. If caching is enabled, the resolver system saves a copy of all replies it receives from DNS servers. Next time, if it receives a query for the same name, instead of forwarding the query to DNS servers, it uses locally saved copies to answer the query.
Example of DNS resolver system
Suppose, a system wants to know the IP address of Google.com. For this, it creates a query to know the IP address associated with the name Google.com and sends that query to the resolver system.
If the resolver system is a DNS server, it checks its database, finds the IP address associated with the name Google.com, creates a reply message that includes the IP address associated with the name Google.com, and sends that message back to the system which sent the query message.
If the resolver system is not a DNS server, then it forwards that query to all configured DNS servers in a sequence until it gets the IP address of the name it is looking for.
The sender system learns the IP address of Google.com from the reply message it receives from the resolver system and uses that IP address to access Google.com.
Conclusion
A resolver system is a vital component of a network that helps in resolving names with IP addresses. It reduces the burden of managing records in the hosts file from other computers, reduces the number of DNS servers' IP addresses required to be configured on each network system, and improves network performance and efficiency. It is either a DNS server or a system configured to communicate with DNS servers to resolve IP addresses.