It's Geek Christmas!
Today in 1969 the first computer-to-computer link; the link was accomplished through
ARPANET (Advanced Research Projects Agency Network). It became the forerunner of the Internet.
And to this day, if you peep under the hood of the technologies that hold our modern internet together, you'll find the four letters ARPA.
My favourite example is the reverse DNS zones.
Forward DNS turns a human-friendly name into an IP address. E.g.
www.google.com is 216.58.198.68.
Reverse DNS is designed to do the opposite, to turn an IP address into a human-friendly name. Reverse DNS uses the DNS system, so someone had to come up with a scheme for encoding an IP as a DNS name. For various reasons that do actually make sense on deeper inspection, the rule is simple, take the IP, reverserve the order of the four numbers (not the digits, the four numbers as blocks), and append .inaddr.arpa to the end.
So, the reverse DNS name for the IP address 216.58.198.68 is 68.198.58.216.in-addr.arpa
So, today, in 2016, the top-level domain for all reverse DNS lookups is arpa! That just goes to show just how pivotal the ARPANet was in the design and implementation of what we now call the Internet.
B.