I am going to take credit for 4.2.2.2 being used as a DNS server entry in your router... here's the story-
In 1998, I was managing a network operations center with a few support technicians. Early on in training these guys, I told them to ping 4.1.1.1 to see if the Internet was 'up', because 4.1.1.1 seemed like the "411" from phone calling... easy to remember when you were panicky (as they could become when our network had problems).
One day 4.1.1.1 stopped responding to pings, and we freaked out for a second- but only it was down. I immediately responded with, "Well, then what about 4.2.2.2?", just incrementing the 1's to 2's. It NEVER went down. It soon became our defacto test host to ping.
After a very short while, we were curious as to what this address was used for... and not being from the NE where it was originally used in the GTE network, we didn't already know it was a secondary caching-only resolver. But we soon found out... and also found that it was usable from outside GTE's network. So when we needed a quick DNS server to use ... we used 4.2.2.2.
I think it spread- not only as a DNS server to use, but also as a ping host test. I've definitely used it in my network administration career and told others to use it. But to hear it come back as a suggestion to me makes me smile.
Personally I think it's insecure that Level3 (which now controls it) allows it to continue to resolve for clients outside of it's network... but that doesn't stop me from using it
Dan Farrell
dannosite.com