Ping Online - IPv4 & IPv6

What you should know about ICMP (Ping).

The Internet Control Message Protocol (ICMP) is used in computer networks to exchange information and error messages via the Internet Protocol in version 4 (IPv4). A similar protocol called ICMPv6 exists for IPv6.

ICMP is part of IPv4, but is treated as an independent protocol. Every router and computer is expected to "understand" ICMP. Most ICMP packets contain diagnostic information: They are sent back to the source by the router when the router drops packets, for example because the destination is unreachable or the TTL has expired. The following principles apply:

• ICMP uses IP as the communication base by interpreting itself as a higher layer protocol, i.e. ICMP messages are encapsulated in IP packets.
• ICMP detects some error conditions, but does not make IP a reliable protocol.
• ICMP analyzes errors in every IP packet except those carrying an ICMP message.
• ICMP messages are not sent in response to packets to destination addresses that are multicast or broadcast addresses.
• ICMP messages reply only to a unique source IP address.