ICMP — The Error Messages That Explain the Network

ICMP is Layer 3 error and diagnostic messaging — not TCP/UDP, and not a transport for data. Type Meaning You meet it in 0 / 8 Echo reply / request ping 3 Destination unreachable codes: 0 net, 1 host, 3 port, 4 fragmentation needed (PMTUD) 11 Time exceeded every traceroute hop (TTL hits 0) Reading […]