Since most networks have evolved over
time, they are frequently odd collections of equipment for which no
single tool may be ideal. And even when the same tool can be used,
differences in equipment may necessitate minor differences in how the
tool is used. Since many of the tasks may need to be done on a
regular basis, it should come as no surprise that scripting languages
are a popular way to automate these tasks. Getting started can be
labor intensive, but if your current approach is already labor
intensive, it can be justified.
You will want to use a scripting language with extensions that
support the collection of network data. To give an idea of this
approach,
and its extensions are briefly
described here. Even if you don't really want to write your own
tools, you may want to consider one of the tools based on
. Of course, there
are other scripting languages that you may want to consider. Perl is
an obvious choice. Several packages and extensions are available for
system and network administration. For example, you may want to look
at
. This is a set of Perl scripts that
do network scans. For SNMP-based management, you'll probably
want to get Simon Leinen's SNMP extensions
6.4.1. Tcl/Tk and scotty
Tool Command Language, or
Tcl
(pronounced "tickle"), is a scripting language that is
well suited for network administration.
Tcl was
developed in the late 1980s by John Ousterhout, then a faculty member
at UC Berkeley.
Tcl was designed to be a
generic, embeddable, and extensible interpreted language. Users
frequently cite studies showing
Tcl requires
one-tenth the development time required by C/C++. Its major weakness
is that it is not well suited for computationally intensive tasks,
but that shouldn't pose much of a problem for network
management. You can also write applets or
tclets
(pronounced "tik-lets") in
Tcl.
Tcl can be invoked interactively using the
shell
tclsh (pronounced "ticklish")
or with scripts. You may need to include a version number as part of
the name. Here is an example:
bsd2# tclsh8.2
%
This really is a shell. You can change
directories, print the working directory, copy files, remove files,
and so forth, using the usual Unix commands. You can use the
exit command to leave the program.
One
thing that makes
Tcl interesting is the number
and variety of extensions that are available.
Tk
is a set of extensions that provides the ability to create GUIs in an
X Window environment. These extensions make it easy to develop
graphical interfaces for tools.
Tk can be
invoked interactively using the windowing shell
wish. Both
Tcl and
Tk are implemented as C library packages that
can be included in programs if you prefer.
scotty,
primarily the work of Jürgen Schönwälder, adds network
management extensions to
Tcl/Tk. The
tnm portion of
scotty adds
network administration support. The
tkined
portion of
scotty, described in the next
section, is a graphical network administration program. What
tnm adds is a number of network management
commands. These include support for a number of protocols including
ICMP, UDP, DNS, HTTP, Sun's RPC, NTP, and, most significantly,
SNMP. In addition, there are several sets of commands that simplify
writing network applications. The
netdb command
gives access to local network databases such as
/etc/hosts, the
syslog
command supports sending messages to the system logging facilities,
and the
job command simplifies scheduling tasks.
A few examples should give an idea of how these commands could be
used.
You can invoke the
scotty interpreter directly
as shown here. In this example, the
netdb
command is used to list the
/etc/host table on a
computer:
bsd4# scotty
% netdb hosts
{localhost.lander.edu 1.0.0.127} {bsd4.lander.edu 239.63.153.205} {bsd4.lander.e
du. 239.63.153.205} {bsd1.lander.edu 231.60.153.205} {sol1.lander.edu 233.60.153
.205} {lnx1.lander.edu 234.60.153.205}
% exit
The results are returned with each entry reduced to the canonical
name and IP address in brackets. Here is the host table for the same
system:
bsd4# cat /etc/hosts
127.0.0.1 localhost.lander.edu localhost
205.153.63.239 bsd4.lander.edu bsd4
205.153.63.239 bsd4.lander.edu.
205.153.60.231 bsd1.lander.edu bsd1
205.153.60.233 sol1.lander.edu sol1
205.153.60.234 lnx1.lander.edu lnx1
Note that there is not a separate entry for the alias bsd4.
Here are a few examples of other commands. In the first example, the
name of the protocol with a value of 1 is looked up in
/etc/protocols using the
netdb command:
% netdb protocols name 1
icmp
In the second example, a reverse DNS lookup is done for the host at
205.153.63.30:
% dns name 205.153.63.30
sloan.lander.edu
Finally, an ICMP ECHO_REQUEST is sent to
www.cisco.com:
% icmp echo www.cisco.com
{www.cisco.com 321}
The response took 321 ms. Other commands, such as
snmp, require multiple steps to first establish
a session and then access information. (Examples are given in
Chapter 7, "Device Monitoring with SNMP".) If you are interested in using these tools
in this manner, you will first want to learn
Tcl. You can then consult the manpages for these
extensions. A number of books and articles describe
Tcl, some of them listed in
Appendix B, "Resources and References". The source is freely available for all these
tools.
