| Summary

| An understanding of the following key points should have been achieved: IP is a best-effort delivery method that uses ICMP messages to alert the sender that the data did not reach its destination. ICMP echo request and echo reply messages allow the network administrator to test IP connectivity to aid in the troubleshooting process. ICMP messages are transmitted using the IP protocol so their delivery is unreliable. ICMP packets have their own special header information starting with a type field and a code field. Identify potential causes of specific ICMP error messages The functions of ICMP control messages ICMP redirect/change request messages ICMP clock synchronization and transit time estimation messages ICMP information request and reply messages ICMP address mask request and reply messages ICMP router discovery message ICMP router solicitation message ICMP congestion and flow control messages