Monday 29 June 2015

How ping command works

    • The Internet Ping program works much like a sonar echo-location, sending a small packet of information containing an ICMP ECHO_REQUEST to a specified computer, which then sends an ECHO_REPLY packet in return. 
    • The IP address 127.0.0.1 is set by convention to always indicate your own computer.
    • Therefore, a ping to that address will always ping yourself and the delay should be very short. This provides the most basic test of your local communications.

    The ping command is a very common method for troubleshooting the accessibility of devices. It uses a series of Internet Control Message Protocol (ICMP) Echo messages to determine:
    • Whether a remote host is active or inactive.
    • The round-trip delay in communicating with the host.
    • Packet loss.
    The ping command first sends an echo request packet to an address, then waits for a reply. The ping is successful only if:
    • the echo request gets to the destination, and
    • the destination is able to get an echo reply back to the source within a predetermined time called a timeout. The default value of this timeout is two seconds on Cisco routers.


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