Pinger
 What
does it do?
Pinger is a very simple implementation of the ICMP (Internet Control
Message Protocol) protocol. It allows you to test connectivity and response
times across a network or the Internet.
How does it work?
Pinger sends a small string of data to a target host a set number of
times at a set interval. It will then count the time it takes for that
packet to return from the target and if it takes longer than a set timeout
value, it is discarded.
How do I use it?
Note: Because ICMP sockets can only be opened
by root-processes, you can only use the "legacy" ping tool
(shown on the left) when authenticated. If you aren't authenticated,
you will only be able to use the text-based ping tool. See Using Net
Tool Box for more information on authentication.
In Net Tool Box, click the "Pinger" button on
the toolbar. When the Ping window appears, type the DNS name or IP address
of the target in the "Target" field. If you want to change
the number of times the host is pinged, change the "Count"
field to your preferred value. Also, if you know your network is particularly
slow or fast, change the "Timeout" value as required. Also,
if you want to increase or decrease the interval between pings, change
the "Interval" field.
Once you have set the values press "Start". Pinger will then
start sending the packets. When a packet has been sent a row will be
added to the list with the packet number in the second column. Once
a packet has been received, it will display a tick in the "Received"
column and the time it took (in milliseconds) in the "Time"
column. If a packet has not been received in less than the timeout value,
it will be marked with a "X" in the "Received" column.
If you are using the textual-based ping tool, the results will not be
shown in the same way. They will appear as text with each line describing
the state in which each packet was received. One benefit of the textual
ping tool is that it allows you to ping your subnet for responses (instead
of one machine). To do this you should try entering your broadcast address
as the target. Your broadcast address can be found in the Interfaces
window.
Problems
ICMP packets cannot go backwards through a NAT (Network Address Translation)
firewall or router. That means that if the address you are trying to
ping has an IP starting with either "10.x.x.x" or "192.168.x.x" and
you are not on the same network, the pings will always fail.
Also, some firewalls discard all ICMP packets for security. This
is because more complex implementations of ICMP can be used maliciously.
A common malicious use of ICMP is known as the "Ping of Death".
On older computers this can crash the network interfaces and sometimes
the whole operating system, which is fatal for servers. Now it is
very rare to have a problem with ICMP attacks, however they do happen
(to my ISP anyway).
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