My favorite IP address 4.2.2.1
The most common question I need to answer when I am at the console of a machine is: “Does this machine have basic network connectivity?”. While there are a lot of ways to accomplish this, I find the most convenient cross platform way to do this is with the ping command. The question then becomes, what should I ping?
The answer depends on what you are trying to accomplish. In most cases, I am troubleshooting this hosts connectivity to the network (not the core network itself) so any IP on the internal LAN or out on the Internet will do (most networks I work on do have Internet connectivity such that I can ping Internet hosts).
Many would say you should start with the most basic test and try to ping your gateway address (which I agree with), but this requires some thought on my part to figure out what subnet I am on and then type out some ip like 192.168.1.1 or 172.16.2.1. I find these IP’s difficult to type, and so I generally go to my favorite standby 4.2.2.1.
The IP 4.2.2.1 is wonderful since it happens to be a DNS server for Level 3 communications (or maybe Verizon, not quite sure which since the IP space is registered to L3, but the reverse DNS points at gtei.net which rolled into Verizon, and back in the day I am pretty sure it was a GTE DNS server). Since it is a DNS server for one of the largest networks in the world it is *always* available, and I think it is actually implemented as an “anycast” IP which means there are many servers around the world serving out responses to that IP and you will be routed to whichever is closest network wise.
Not only is it a great host to ping to check network connectivity, but it is also a recursive DNS server that will respond to queries from any host on the Internet! This is useful when you are on some network somewhere and you don’t know what DNS servers to use (or don’t want to use the local ones for some reason), and just need something as a temporary solution.
Now please don’t go ping flooding these dns servers or using them for all your networks recursive DNS queries. I very much appreciate that Level 3 lets these servers respond to recursive queries (which I don’t think they did at one time in the past) and I don’t want to give them a reason to turn it off!
It’s also worth noting that 4.2.2.2 and 4.2.2.3 also respond similarly. It might actually be faster to type 4.2.2.2 than 4.2.2.1, but I am so used to the latter that it is what I use.
-Eric
L3 bought Genuity/BBN/GTE Enterprise
http://www.isp-planet.com/news/2002/lvlt_genu_021129.html
http://www.cybertelecom.org/industry/genuity.htm
4.2.2.1-4.2.2.6 all work as recursive DNS and many are unicast. Verizon before they bought MCI was really in bed with L3 for dark fiber which they continue to still use. The reverse DNS entries might change for 4.2.2.1 etc at a later date but the IP and network is Level 3.