Ping strangeness is a term used in troubleshooting to describe the incidence of an unusual pattern of ICMP ECHO_REQUEST packets being sent to a specific network node or an unusual number of error messages returning.
Ping (Packet Internet Groper) is a utility program that allows a user or program to verify that a particular IP address exists and can accept requests. Ping can be used as an alternative to the traceroute utility to troubleshoot network connectivity and latency issues. It is faster than traceroute and generates less network traffic.
When a user issues a ping request, the program formats an ICMP ECHO_REQUEST packet and sends it to a designated target address. If the remote IP address is active, it responds with an ICMP ECHO_REPLY packet. Ping then uses the timestamp of the Echo Reply to calculate a round-trip time and gauge response time.
If the target address is unavailable or something else is not working normally, Ping will report an error. Common errors include Destination Unreachable, Unknown Host and Request Timed Out.
When there is an unusual pattern of ICMP ECHO_REPLY packets being sent to the same server in the same time period, or there is an unusual number of error messages, this "strange" pattern is worth investigating. It could be that Ping is being used to carry out a denial of service attack (DoS) or look for attack vectors.