DNS
Network 'address book', the way sites and systems are located
The DNS system is a core part of the Internet and most private networks. It is essentially an
address book mapping the names of computers or websites with the IP
addresses which uniquely identify them and enable them to be contacted.
Networked computers are given a specific DNS server, which they query whenever a website or other
host is needed. The DNS server returns the IP address corresponding to the requested name, which it may have
cached in its own database or it may need to find by querying another DNS server higher up the chain. The IP
address then allows the computer to contact the system it wants.
DNS is often manipulated by malware and cybercriminals, for example by adjusting the
hosts file to block access to security resources or for pharming purposes.
Apart from the IP address of a computer connected to the Internet, DNS is used for various
other purposes, such as to determine the mail server(s) to use to send an email to an address on a certain
domain, or to determine the SPF record for a domain. Anti-spam measures such as
DNSBLs and URIBLs also make use of the DNS protocol.
