Ping packets are ICMP protocol data units (PDUs) encapsulated in the data field (payload) of IP datagrams. As such, the IP software can track individual pings (echo requests) and their responses (echo replies). On a Cisco router you will get the following responses:
| Character | Description |
| ! | Each exclamation point indicates receipt of a successful reply |
| . | Each period indicates the network server timed out while waiting for a reply |
| U | A destination unreachable error PDU was received |
| Q | Source quench (destination is too busy) |
| M | Could not fragment |
| ? | Unknown packet type |
| & | Packet lifetime exceeded |
The actual PING response looks something like this:
router>ping www.yahoo.com Translating "www.yahoo.com"...domain server (209.1.221.10) [OK]
Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 216.115.102.81, timeout is 2 seconds !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 4/16/24ms
The response times for ping are ROUND-TRIP and are cumulative over the
entire path out and back to that destination. The ping tool does not tell
you WHERE the latency or packet loss is being introduced, nor
does it tell you if some sort of queuing stragegem is in place
altering your results. It is therefore highly unreliable and cannot
be trusted for these purposes.
PING is to be used to verify that a host is up and functioning. That is all it was ever intended to do.