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IP is an unreliable method for delivery of
network data. It is known as a best effort delivery mechanism. It
has no built-in processes to ensure that data is delivered in the
event that problems exist with network communication. If an
intermediary device such as a router fails, or if a destination device
is disconnected from the network, data cannot be delivered.
Additionally, nothing in its basic design allows IP to notify the
sender that a data transmission has failed. Internet Control Message
Protocol (ICMP) is the
component of the TCP/IP protocol stack that addresses this basic
limitation of IP.
ICMP does not overcome the unreliability issues in
IP. Reliability must be provided by upper layer protocols if it is
needed.
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