Service Security

Since a port number can be specified on the command line, telnet clients can be used to connect to arbitrary ports on Solaris servers. This makes a telnet client a useful tool for testing whether services that should have been disconnected are actually active. For example, you can interactively issue commands to an FTP server on port 21, this way:

 $ telnet server 21 Trying 172.16.1.1... Connected to server. Escape character is '^]'. 220 server FTP server (UNIX(r) System V Release 4.0) ready. 

And on a sendmail server on port 25:

 $ telnet server 25 Trying 172.16.1.1... Connected to server. Escape character is '^]'. 220 server ESMTP Sendmail 8.9.1a/8.9.1; Mon, 22 Nov 1999     14:31:36 +1100 (EST) 

Interactive testing of this kind has many uses. For example, if we telnet to port 80 on a server, we are usually connected to a web server where we can issue interactive commands using the Hypertext Transfer Protocol (HTTP). For example, to GET the default index page on a server, we could type get index.html :

 Trying 172.16.1.1... Connected to server. Escape character is '^]'. GET index.html <<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">> <<HTML>><<HEAD>> <<TITLE>>Server<</TITLE>><</HEAD>> <<h1>>Welcome to server!<</h1>> 

This technique is useful when testing proxy server configurations for new kinds of HTTP clients (for example, a HotJava browser) or to be executed during a script to check whether the web server is active and serving expected content.

 
 
   


Sun Certified Solaris 9.0 System and Network Administrator
Sun Certified Solaris(tm) 9 System and Network Administrator All-in-One Exam Guide
ISBN: 0072225300
EAN: 2147483647
Year: 2003
Pages: 265
Authors: Paul Watters

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