Full form: Internet Control Message Protocol
Also known as: Internet Control Message Protocol
Quick Definition
A Layer 3 protocol used for network diagnostics and error reporting.
ICMP is a Layer 3 protocol used to send control and error messages between network devices. It is most commonly associated with the ping command (Echo Request/Echo Reply) and traceroute. ICMP does not carry user data and is not a reliable transport protocol. It is defined in RFC 792 and operates directly on top of IP (protocol number 1).
ping 192.168.1.1 traceroute 10.0.0.1
When you ping 8.8.8.8, your host sends ICMP Echo Request packets. If 8.8.8.8 is reachable, it responds with ICMP Echo Reply packets. A 'Destination Unreachable' ICMP message indicates the packet could not be delivered.
ICMP is connectionless and does not guarantee delivery. Firewalls often block ICMP, so a failed ping does not always mean the host is down.
ICMP is a Layer 3 protocol used to send control and error messages between network devices. It is most commonly associated with the ping command (Echo Request/Echo Reply) and traceroute. ICMP does not carry user data and is not a reliable transport protocol. It is defined in RFC 792 and operates directly on top of IP (protocol number 1).
ICMP is connectionless and does not guarantee delivery. Firewalls often block ICMP, so a failed ping does not always mean the host is down.
When you ping 8.8.8.8, your host sends ICMP Echo Request packets. If 8.8.8.8 is reachable, it responds with ICMP Echo Reply packets. A 'Destination Unreachable' ICMP message indicates the packet could not be delivered.
ICMP falls under the Network Fundamentals domain of the 200-301 exam. Understanding it in context with related terms like tcp and udp is essential for answering scenario-based questions correctly.