Ping

• Originally developed in 1982 to do general reachability testing

• • If you can’t ping a host, you may not have connectivity with it
  • • Not always the case…some firewalls block pings
  • Also very useful for measuring roundtrip delay and loss between two hosts

• Ping uses the ICMP echo request and echo reply messages

• Clients are application layer programs

• • They use “raw sockets” to talk directly to the IP layer

• There are no “ping servers”

• • Ping responses are handled in the target’s ICMP layer