block telnet to specific port Post: 17865

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Special Forums IP Networking block telnet to specific port Post 17865 by thomas.jones on Wednesday 20th of March 2002 07:51:00 PM

03-20-2002

Registered User

First of all, the standard telnet port is 23. If you have telnet enabled through inetd.conf...then it's probably the default port of 23. Now to stop port 80 access it's just a little different.

If you had a webserver available on your node....then a person telnetting to it will get the httpd system banner:

**********************
Whatever Linux v2.2.14
Apache vX.X.XX
etc.
**********************

They can then send a GET command using telnet to pull the HTML...this is exactly what a web browser does.

To stop someone from connecting to this port...all you have to do is go into inetd.conf and comment out the HTTP line....which should look something like this:

http stream tcp nowait nobody ?/var/www/server/httpd httpd

This will shutdown the daemon...or "service"......then no one will be able to connect to it. Restart the inetd daemon by issuing the following command:

killall -HUP inetd

BTW, you will NOT be able to block a telnet'd connection to your port....and allow a web browser. To the firewall, they are essentially the same traffic. [TCP from a 1024+ port]

HTH.

Last edited by thomas.jones; 03-20-2002 at 09:01 PM..

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LEARN ABOUT DEBIAN

micro_proxy

micro_proxy(8)						      System Manager's Manual						    micro_proxy(8)

NAME

       micro_proxy - really small HTTP/HTTPS proxy

SYNOPSIS

       micro_proxy

DESCRIPTION

       micro_proxy  is	a  very small HTTP/HTTPS proxy.  It runs from inetd, which means its performance is poor.  But for low-traffic sites, it's
       quite adequate.	It implements all the basic features of an HTTP/HTTPS proxy, in only 260 lines of code.

       To install it, add a line like this to /etc/inetd.conf:
	   webproxy  stream tcp nowait nobody  /usr/sbin/micro_proxy micro_proxy
       Make sure the path to the executable is correct.  Then add a line like this to /etc/services:
	   webproxy   port/tcp
       Change "port" to the port number you want to use - 3128, or whatever.  Then restart inetd by sending it a "HUP" signal, or rebooting.

       On some systems, inetd has a maximum spawn rate - if you try to run inetd services faster than a certain number of  times  per  minute,	it
       assumed	there's  either  a  bug of an attack going on and it shuts down for a few minutes.  If you run into this problem - look for syslog
       messages about too-rapid looping - you'll need to find out how to increase the limit.  Unfortunately this varies from OS to OS.	 On  Free-
       BSD,  you  add  a  "-R 10000" flag to inetd's initial command line.  On some Linux systems, you can set the limit on a per-service basis in
       inetd.conf, by changing "nowait" to "nowait.10000".

AUTHOR

       Copyright (C) 1999 by Jef Poskanzer <jef@mail.acme.com>. All rights reserved.

								   16 March 1999						    micro_proxy(8)

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