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TCP/IP Communication Verification Utility (ping/ping6)
(Page 2 of 5)
Operation of the ping Utility
The ping utility is implemented
using ICMP Echo (Request) and Echo Reply messages. As
explained in the
topic discussing these message types,
they are designed specifically for these sorts of diagnostic purposes.
When Device A sends an ICMP Echo message to device B,
device B responds by sending an ICMP Echo Reply message
back to device A. The same functionality exists in ICMPv6, the
IPv6 version of ICMP; the ICMPv6
Echo and Echo Reply messages only differ
from the IPv4 ones slightly in their field structure.
This would seem to indicate that
ping would be an extremely simple utility that would send one
Echo message and wait to see if an Echo Reply was received
back; if so, then this would provide that the two devices were able
to communicate, and if not, this would indicate a problem somewhere
on the internetwork between the two. However, almost all ping
implementations are much more complex than this. They use multiple sets
of Echo and Echo Reply messages, along with considerable
internal logic, to allow an administrator to determine all of the following,
- Whether or not the two devices can communicate;
- Whether congestion or other problems exist that
might allow communication to succeed sometimes but cause it to fail
in others, seen as packet lossif so, how bad the loss is;
- How much time it takes to send a simple ICMP
message between devices, which gives an indication of the overall latency
between the hosts, and also indicates if there are certain types of
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Version 3.0 - Version Date: September 20, 2005
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