FG Ping

The purpose of this Ping implementation initially was to demonstrate the use of the Windows ICMP library. While it's still a good example in this regard it is also worth it in itself as a powerful ping utility. It's behavior was closely modeled after that of Linux with some extensions taken from traceroute.

The Ping application uses the ICMP protocol's mandatory ECHO_REQUEST datagram to elicit an ICMP ECHO_RESPONSE from a host or gateway. ECHO_REQUEST datagrams (``pings'') have an IP and ICMP header, followed by a ``struct timeval'' and then an arbitrary number of ``pad'' bytes used to fill out the packet.

In trace mode Ping will print the route packets take to reach the specified network host. The Internet is a large and complex aggregation of network hardware connected together by gateways.

Tracking the route one's packets follow (or finding the miscreant gateway that's discading your packets) can be difficult. In trace mode Ping uses the IP protocol ``time to live'' field and attempts to elicit an ICMP_ TIME_EXCEEDED response from each gateway along the path to some host.