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TCP/IP Communication Verification Utility (ping/ping6)
(Page 4 of 5)
Methods of Diagnosing Connectivity Problems Using ping
Most people find that using ping
with default settings is enough for their needs. In fact, the utility
can be used in this simplest form to perform a surprising number of
diagnostic checks. In many cases, the ping command can be used
to diagnose connectivity problems by using it multiple times in sequence,
often starting with checks at or close to the transmitting device and
then proceeding outwards towards the other device with which the communication
problem has been observed. Some examples of how ping can be used
in this way:
- Internal Device TCP/IP Stack Operation:
By performing a ping on the devices own address, you can
verify that its internal TCP/IP stack is working. This can also be done
using the standard IP loopback address, 127.0.0.1.
- Local Network Connectivity: If the internal
test succeeds, its a good idea to do a ping on another
device on the local network, to verify that local communication is possible.
- Local Router Operation: If there is no
problem on the local network, it makes sense to ping whatever
local router the device is using to make sure it is operating and reachable.
- Domain Name Resolution Functionality:
If a ping performed on a DNS domain name fails, you should try
it with the devices IP address instead. If that works, this implies
either a problem with domain name configuration or resolution.
- Remote Host Operation: If all the preceding
checks succeed, you can try pinging a remote host to see if it
responds. If it does not, you can try a different remote host; if that
one works, it is possible that the problem is actually with the first
remote device itself and not with your local device.
Note: While the inability to get a response from a device to a ping has traditionally been interpreted as a problem in communication, this is not always necessarily the case. In the current era of increased security consciousness, some networks are set up to not respond to Echo messages, to protect against attacks that use floods of such messages. In this case a ping will fail, even though the host may be quite reachable.
Key Concept: The TCP/IP ping utility is used to verify the ability of two devices on a TCP/IP internetwork to communicate. It operates by having one device send ICMP Echo (Request) messages to another, which responds with Echo Reply messages. The program can be helpful in diagnosing a number of connectivity issues, especially if it is used to test the ability to communicate with other devices in different locations. It also allows the average round-trip delay to exchange messages with another device to be estimated.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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