The Internet Control Message Protocol (ICMP) detects and reports network error conditions. ICMP reports on the following:
Dropped packets – Packets that arrive too fast to be processed
Connectivity failure – A destination system cannot be reached
Redirection – Redirecting a sending system to use another router
Chapter 7, Administering a TCP/IP Network (Tasks) contains more information on the Solaris OS commands that use ICMP for error detection.