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Packet Internet Groper (Ping)<br />

Ping began as a simple IP-based UNIX <strong>to</strong>ol for testing host reachability. Over time,<br />

it has evolved, like many o<strong>the</strong>r "simple" UNIX <strong>to</strong>ols, <strong>to</strong> o<strong>the</strong>r operating systems and<br />

even <strong>to</strong> support reachability testing for o<strong>the</strong>r Layer 3 pro<strong>to</strong>cols (IPX, AppleTalk, and<br />

so on). As an IP application, ping functions by sending ICMP echo_request<br />

messages at a target destination host. When <strong>the</strong> target host receives <strong>the</strong>se packets,<br />

it responds <strong>to</strong> <strong>the</strong> source host with ICMP echo_reply messages.<br />

The initial UNIX implementation of ping simply indicated if <strong>the</strong> host was reachable.<br />

Today, most UNIX-based implementations of ping transmit an infinite stream of<br />

ICMP messages at <strong>the</strong> target host. This action is terminated using <strong>the</strong> Ctrl+C<br />

keystroke combination. Alternatively, ping implementations that come with Cisco<br />

IOS and Windows by default only transmit a short burst (The IOS version sends five<br />

ICMP requests and Windows version sends four.). The ping command output<br />

example below illustrates <strong>the</strong> basic information you should expect <strong>to</strong> be returned<br />

from most ping implementations:<br />

thor# ping 192.168.55.1<br />

PING 130.140.55.1 (130.140.55.1): 56 data bytes<br />

64 bytes from 192.168.55.1: icmp_seq=0 ttl=30 time=1.164 ms<br />

64 bytes from 192.168.55.1: icmp_seq=1 ttl=30 time=0.918 ms<br />

64 bytes from 192.168.55.1: icmp_seq=2 ttl=30 time=0.983 ms<br />

64 bytes from 192.168.55.1: icmp_seq=3 ttl=30 time=0.939 ms<br />

64 bytes from 192.168.55.1: icmp_seq=4 ttl=30 time=0.945 ms<br />

64 bytes from 192.168.55.1: icmp_seq=5 ttl=30 time=0.946 ms<br />

64 bytes from 192.168.55.1: icmp_seq=6 ttl=30 time=0.932 ms<br />

^C<br />

—- 192.168.55.1 ping statistics —-<br />

7 packets transmitted, 7 packets received, 0% packet loss<br />

round-trip min/avg/max = 0.918/0.975/1.164 ms<br />

thor#<br />

NOTE<br />

In most cases, ping comes as part of an operating system's standard TCP/IP<br />

implementation. As a rule, UNIX ping implementations are more feature-rich than<br />

<strong>the</strong>ir Windows and Macin<strong>to</strong>sh (which has no native implementation) counterparts.<br />

There are, however, a number of great add-on <strong>to</strong>ols available on <strong>the</strong> Internet. Here<br />

is a short list of some ping <strong>to</strong>ols for Mac and PC.

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