How Ping Works ?

Summary:

++++++++++

At this point, you should have a fairly complete understanding of the cycle of processing associated with ping.

Let me recapitulate the essential elements:

• As the ping program initializes, it opens a raw ICMP socket so that it can employ IP directly, circumvent-

ing

TCP and UDP

.

• Ping formats an ICMP type 8 message, an Echo Request, and sends it (using the “sendto” function) to

the designated target address. The system provides the IP header and the data link layer envelope.

¶s ICMP messages are received,

ping has the opportunity to examine each pack

et to pick out those

items that are of interest.

• The usual behavior is to siphon off ICMP type 0 messages, Echo Replies, which have an identification

field v

Link:  http://images.globalknowledge.com/wwwimages/whitepaperpdf/WP_Mays_Ping.pdf

alue that matches the program PID.