DNS in practice, operates with a set of defined resource record types. These allows for different kinds of DNS resolutions to take place.
Used to point a certain domain name at a certain IPv4 IP address
In its most basic use, a single A record is configured for a single domain name, but a single domain name can have multiple A records. This allows for a technique known as DNS round robin to be used to balance traffic across multiple IPs.
A concept that involves iterating over a list of items one by one in an orderly fashion
www.microsoft.com has 4 A records - four IPs.
When a DNS resolver performs a lookup of www.microsoft.com, all four IPs would be returned in the order, first configured.
DNS resolving computer would know that it should try to use the first entry, but it knows about all four just in case a connection fails.
The next computer to perform a look up for www.microsoft.com, would also receive all four ips but the ordering have been changed.
In order of:
This pattern would continue for every DNS resolution attempt to balance traffic.
Another resource record type that’s becoming more popular is the quad A record
Very similar to an A record, except that it returns an IPv6 address instead of an IPv4 address.