Internet Protocols - CCIE Routing and Switching Exam Certification Guide - page 295

Although these examples have successful returns, other test characters can be returned. Table 6-17
shows those characters.

Ping Test Characters Table 6-17

Character Description

! Receipt of a reply.

. The network server timed out while waiting for a reply.

U A destination unreachable error message was received.

Q Source quench (destination too busy).

M Could not fragment.

? Unknown packet type.

& Packet lifetime exceeded.

Telnet

Telnet is a TCP/IP application-layer protocol that provides remote terminal access. RFC 854 is
the current Telnet protocol specification. Telnet runs over TCP, by using TCP port 23 to connect
to the Telnet server. The remote terminal is text based; by default, it uses 128 ASCII codes.

FTP

FTP is a TCP/IP application-layer protocol that provides file transfer capabilities. FTP was first
specified by RFC 114 and has been updated several times, but the standard RFC is 959. The
objectives of the FTP protocol are to provide sharing of files, shield users from variations in file
storage systems among hosts, and transfer data reliably and efficiently.

FTP uses two different connections: One is a control connection between the user and the FTP
server, and the second is a data transfer connection. The data connection might not exist until
the commands to transfer the files are executed. The FTP control connection is established
through a TCP process, and the server port is TCP 21. The data connection uses TCP port 20.

You can use FTP on any Windows system, Unix system, and others.

TFTP

TFTP is a simpler type of FTP. Instead of using TCP as FTP does, it uses UDP as a transport
protocol. TFTP does not use a control connection, it cannot list directories, nor does it have user
authentication. It reads or writes files from/to a remote TFTP server. TFTP (version 2) is defined
in RFC 1350 and uses UDP port 69. An example of the use of TFTP is the transfer of IOS and
configuration files to a router. Chapter 3, “Cisco Equipment Operations,” covers the methods that
you can use to transfer IOS and configuration files from and to a router by using a TFTP server.