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The ICMP header starts after the IPv4 header and is identified by its protocol number, 1. [6] All ICMP packets have an eight-byte header and variable-sized data section. The first four bytes of the header have fixed format, while the last four bytes depend on the type and code of the ICMP packet.
A functionality which lets a computer A find out whether a computer B is reachable and responding is built into the Internet Control Message Protocol (ICMP). Through an "Echo Request" Computer A asks B to send back an "Echo Reply". [2] These two messages are also sometimes called "ping" and "pong" for historical purposes. [citation needed]
A stateful firewall keeps track of the state of network connections, such as TCP streams, UDP datagrams, and ICMP messages, and can apply labels such as LISTEN, ESTABLISHED, or CLOSING. [2] State table entries are created for TCP streams or UDP datagrams that are allowed to communicate through the firewall in accordance with the configured ...
Pinging involves sending an ICMP echo request to the target host and waiting for an ICMP echo reply. The program reports errors, packet loss , and a statistical summary of the results, typically including the minimum, maximum, the mean round-trip times, and standard deviation of the mean.
In IPv6 this is the only standards-based form to denote network or routing prefixes. For example, the IPv4 network 192.0.2.0 with the subnet mask 255.255.255.0 is written as 192.0.2.0 / 24 , and the IPv6 notation 2001:db8:: / 32 designates the address 2001:db8:: and its network prefix consisting of the most significant 32 bits.
ICMP tunneling works by injecting arbitrary data into an echo packet sent to a remote computer. The remote computer replies in the same manner, injecting an answer into another ICMP packet and sending it back. The client performs all communication using ICMP echo request packets, while the proxy uses echo reply packets.
ICMP hole punching is a technique employed in network address translator (NAT) applications for maintaining Internet Control Message Protocol (ICMP) packet streams that traverse the NAT. NAT traversal techniques are typically required for client-to-client networking applications on the Internet involving hosts connected in private networks ...
Traceroute can help identify incorrect routing table definitions or firewalls that may be blocking ICMP traffic, or high port UDP in Unix ping, to a site. [ clarify ] A correct traceroute response does not guarantee connectivity for applications as a firewall may permit ICMP packets but not permit packets of other protocols.