Ping and ICMP Error
Messages
Ping is a network tool mainly used to test whether a host is
reachable across an IP network and to measure the round-trip time for packets
sent from source to the destination computer. Ping works by sending Internet
Control Message Protocol (ICMP) echo request packets to the destination host
and waits for an ICMP response. It also measures the time it takes for the
packets to return.
When you are unable to “ping” the destination host either by
IP Address or by hostname, you should pay close attention to the results
provided by ICMP. Different messages indicate different types of issues. The
three most common error messages that you will see are as follows:
Destination Host Unreachable
Request Timed Out
Ping Request Could Not Find Host...
Within the ICMP header, you can find more information about
the type and code. If you were to examine the ICMP packets containing these
messages, more details regarding error message can be discovered. You can refer
to this IANA link for more information regarding types and codes for
ICMP. http://www.iana.org/assignments/icmp-parameters
If the ping command is successful in reaching the
destination computer, an examination of the packets sent and received will only
show Echo Requests (type 8) and Echo Replies (type 0)
Destination Host
Unreachable
(type 3, codes 0-15)
The Destination Host Unreachable error message indicates
that a route to the destination node cannot be found. To resolve this problem,
you might need to examine the routing information on the local host to confirm
that the local host is correctly configured. Common issues that generate this
type of error message is the local host not configured with a default gateway.
If the local computer's TCP/IP configuration is correct, you can still receive
this message from your gateway. This would indicate that your gateway does not
have information in the routing table to successful route the packet to the
destination host.
Request Timed Out
(type 11, codes 0-1)
The Request Timed Out error message is very common when you
use the ping command. Essentially, this error message indicates that your host
did not receive the ICMP Echo Reply back from the destination node within the
designated time period. Assuming network connectivity is not the source of the
problem, this is generally an indication that the destination node is not
connected to the network, powered off, or is not configured correctly in
regards to its TCP/IP configuration. It is possible to encounter these messages
when there is heavy congestion on the network since ICMP packets are commonly
treated with the lowest priority on the network.
Ping Request Could
Not Find Host...
(none)
If you see this error message, PING was unable to determine
the IP address from the hostname provided. Either there was a typo in the
hostname, or your name resolution process failed in resolving the IP address
for the hostname provided. Check to make sure the hostname is correct.