| Overview

IP is limited because it is a best effort delivery system. It has no mechanism to ensure that the data is delivered, regardless of the problems it may encounter on the network. Data may fail to reach its destination for a variety of reasons, such as hardware failure, improper configuration or incorrect routing information. To help identify these failures, IP uses the Internet Control Message Protocol (ICMP) to notify the sender of the data that there was an error in the delivery process. This module describes the various types of ICMP error messages and some of the ways they are used. Because IP does not have a built-in mechanism for sending error and control messages, it uses the ICMP to send and receive error and control messages to hosts on a network. This module focuses on control messages, which are messages that provide information or configuration parameters to hosts. Knowledge of ICMP control messages is an essential part of network troubleshooting and is a key to a full understanding of IP networks. Students completing this module should be able to: Describe ICMP Describe the ICMP message format Identify ICMP error message types Identify potential causes of specific ICMP error messages Describe ICMP control messages Identify a variety of ICMP control messages used in networks today Determine the causes for ICMP control messages