Using "loopback.dnsp.co"

loopback.dnsp.co (or loop.dnsp.co) generates a time-based CNAME, and also resolves that CNAME to the localhost address. (either 127.0.0.1 or ::1 as appropriate)

This is a two step process, however the idea here is that you can use the "ping" utility to quickly do both steps at once. Comparing the results to the current time will let you know if you are receiving fresh DNS results, and the deterministic nature of the CNAME will prevent it from having been previously cached. Resolving to the loopback address prevents both confusing timeouts as well as preventing icmp from the test from leaving your machine. (For instance pinging 'random.dnsp.co' could send icmp traffic anywhere)

The CNAME result itself should match the current server time, you will have to correct for time zones etc in your head.


Examples:

prompt> ping loopback.dnsp.co Pinging Wed_04_Mar_2015_23_02_16_090198.loop.dnsp.co [127.0.0.1] with 32 bytes of data: Reply from 127.0.0.1: bytes=32 time<1ms TTL=128 Reply from 127.0.0.1: bytes=32 time<1ms TTL=128 Reply from 127.0.0.1: bytes=32 time<1ms TTL=128 Reply from 127.0.0.1: bytes=32 time<1ms TTL=128 Ping statistics for 127.0.0.1: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 0ms, Maximum = 0ms, Average = 0ms