when people say that they sent a ping packet, they really mean that they sent an ICMP Echo
Request. These two messages are very much self-explanatory. The Echo Request simply means
that the host to which it is addressed should reply to the packet. The Echo Reply is the ICMP
message type that should be used in the reply. The Request includes some data, which can be
specified by the ping command; whatever data is sent in the Echo Request is sent back in the
Echo Reply.
For instance, the ping command enables you to specify the length as well as the source and
destination address, and it also enables you to set other fields in the IP header. Example 5-6,
later in this chapter, shows a good example of the capabilities of the ping command.
file transfer protocols in a typical IP network. Most users use FTP, whereas router and switch
administrators use TFTP. Which is "better" depends partially on what is being done. A more
important question may typically be, "Which is supported on the devices that need to transfer
the file?" Given a choice today, most users will choose FTP because it has many more robust
features. TFTP is a favorite of router administrators, however, because the IOS does not support
FTP as an application.