Lecture 21: Network Management #1

Echo Request

The basic connectivity tool is the availability of the echo request packet type in virtually all network-layer protocols.

In IP, the echo request type is supplied by ICMP, the Internet Control Message Protocol, which is required to be "built-in" to every IP implementation. ICMP is internal to IP: few "hooks" are available for users to generate ICMP packets.

The notable exception is provided by the user program ping, the "Packet INternet Groper".

Ping generates one (or more, see later) ICMP "echo request" packets (IP datagrams) addressed to a specified remote host. On receipt of such a packet, the remote host is required to send a time-stamped "echo reply" packet to the originating host.

Such a transaction confirms packet delivery (ie, the remote host is "reachable") and is "up" (the remote host's operating system is running, and was able to generate the ping reponse). Ping is the single most important frontline weapon of the intelligent network manager...

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