DNS - Domain Name System. Internet service that maps Internet domains into corresponding IP addresses. DNS database is distributed and replicated among many DNS servers, so when you change your domain's IP address, the changes take a while to propagate.

You may be able to identify the domain name of a spammer sending you spam email or the domain name of a computer trying to break into your firewall. You can then use a WHOIS service to get more information about the domain registration information including telephone numbers and addresses of the domain owner. This service converts an Internet IP address of the form xxx.xxx.xxx.xxx to host name by searching domain name service tables.

Ping is a simple program that attempts to make a very basic kind of connection to a target machine. It provides a basic test of whether a particular host is operating properly and is reachable on the network from the testing host. It also provides estimates of the round-trip time and packet loss rate between the hosts. It works by sending ICMP packets to the target host and listening for replies. If the target machine responds ping alerts you that it is "alive", otherwise ping returns a message that the machine is unreachable. Note that the ability to ping a machine does not mean that the machine is fully functional, but it does indicate that the network path to that machine (including all routers between you and the machine) are up and functioning.

To check if a host is up and running on a network. Ping is a command that sends out a packet of data and tests to see if the other host replies back. Often used to check the integrity of a network or internetwork. Derived from the sound that a sonar system makes. A trace-route uses ping to follow the path from host to host to the intended destination.