Glossary
GL-4
CLI Reference Guide for the Cisco Secure Access Control System 5.1
OL-18996-01
SSH
Secure Shell. A network protocol in which data is exchanged over a secure channel between two
computers. Encryption provides confidentiality and integrity of data. SSH uses public-key
cryptography to authenticate the remote computer and allow the remote computer to authenticate the
user.
SSH is typically used to log in to a remote machine and execute commands; but, it also supports
tunneling, forwarding arbitrary TCP ports, and X Window System (X11) connections. It can transfer
files by using the associated SSH File Transfer Protocol (SFTP) or Secure Copy (SCP) protocols.
An SSH server, by default, listens on the standard TCP port 22. An SSH client program is typically used
for establishing connections to an sshd daemon accepting remote connections. Both are commonly
present on most modern operating systems. Proprietary, freeware, and open-source versions of various
levels of complexity and completeness exist.
SNMP
Simple Network Management Protocol. Network management protocol used almost exclusively in
TCP/IP networks. SNMP provides a means to monitor and control network devices, and to manage
configurations, statistics collection, performance, and security.
SNMPv1
SNMPv1 is a simple request/response protocol. In the SNMPv1 framework, the network-management
system installed a request, and managed devices return responses.
SNMPv2C
The second release of SNMP, described in RFC 1902. It provides additions to data types, counter size,
and protocol operations. SNMPv2C support includes a bulk-retrieval mechanism and more detailed
error message reporting to management stations. The bulk-retrieval mechanism supports the retrieval
of tables and large quantities of information, minimizing the number of round-trip transmissions
required. SNMPv2C improved error-handling support includes expanded error codes that distinguish
different kinds of error conditions; these conditions are reported through a single error code in
SNMPv1. Error return codes now report the error type. Three kinds of exceptions are also reported: No
such object, No such instance, and End of MIB view.
T
TCP
Transmission Control Protocol. Connection-oriented transport-layer protocol that provides reliable
full-duplex data transmission. Part of the TCP/IP protocol stack.
Telnet
Telnet (TELetype NETwork). A network protocol used on the Internet or LAN connections. It was
developed in 1969 beginning with RFC 0015 and standardized as IETF STD 8, one of the first Internet
standards.
The term Telnet also refers to software that implements the client part of the protocol. Telnet clients
have been available on most UNIX systems for many years and are available for virtually all platforms.
Most network equipment and operating systems with a TCP/IP stack support some kind of Telnet
service server for their remote configuration (including ones based on Windows NT). Recently, Secure
Shell has begun to dominate remote access for UNIX-based machines.
Most often, a user telnets to a UNIX-like server system or a simple network device such as a switch.
For example, you might “telnet in from home to check your e-mail at work.” In doing so, you would be
using a Telnet client to connect from your computer to one of your servers. Once the connection is
established, you would then log in with your account information and execute the operating system
commands remotely on that computer, such as ls or cd.
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