Terminal Emulators


Terminal emulators are used for many purposes in network management, including user access to network devices. Obviously, access is useful for configuring and troubleshooting devices. There are also times when information or operations on network devices are not available through SNMP and scripts must be written to access this information or capability through terminal access.

Telnet is the traditional way of obtaining terminal emulation access to network devices. Cisco IOS devices also support remote shell, or rsh.

Cisco IOS software provides two methods for obtaining terminal emulation access in a secure manner: Secure Shell (SSH) and IP Security (IPSec) with Virtual Private Networks (VPN). SSH, which devices are just starting to support, provides much greater security for the connection than Telnet. Cisco IOS devices started supporting SSH in 12.0(5)S. Cisco Catalyst devices don't support SSH as of software version 5.2.

IPSec with VPN provides a standards-based method to implement security and includes the capability to secure a terminal emulation session. Cisco IOS devices started supporting IPSec with VPN in IOS 12.0(5)T.

If a program or script needs to obtain information through a terminal session, it needs to be able to watch for prompts from the device and enter commands at the right time and speed so that they are recognized by the device and do not overrun any input buffers. Such a capability is commonly known as an Expect script, after the Expect language written over the TK/TCL programming language. Expect-like libraries are available for PERL, Java, C, as well as the original TK/TCL program.

See Example 19-9 in Chapter 19, "Frequently Asked Questions," for an example of an Expect script written in PERL.



Performance and Fault Management
Performance and Fault Management: A Practical Guide to Effectively Managing Cisco Network Devices (Cisco Press Core Series)
ISBN: 1578701805
EAN: 2147483647
Year: 2005
Pages: 200

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