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Top Forums Shell Programming and Scripting How to check the IP:PORT firewall uses? Post 303004043 by bakunin on Monday 25th of September 2017 05:11:04 PM
Old 09-25-2017
Quote:
Originally Posted by mohtashims
2. Also, from @Chubler_XL's statement I understand that there is no way to remotely monitor the firewall like we monitor SMTP [port 25] or SSH [port 22].
Correct.

A firewall is not a service, but a software controlling the network operation of a system:

Let us start with a router: a router basically is a system with two network interfaces which stand in different IP-networks and a machinery in between which relays traffice between these two networks from one interface to the other, based on some rules (the "routing table"). Routing takes place on layer 3 of the network and hence the router "operates at layer 3".

A firewall is a similar machinery but operates on (more correctly: on top of) layer 4: again two network interfaces homed in different IP-networks, but the machinery (usually some software - the firewall process) in between operates on layer 4 and relays layer-4-packets (TCP, UDP, and similar protocols) between these two interfaces.

Per default all packets are "not relayed" (blocked) this way. By configuring rules some of these packets are allowed nonetheless and therefore indeed relayed.

There are two fundamental ways such firewalls operate: packet-filtering and stateful inspection.

In packet filtering the rules state which port of a certain IP on one side may communicate with which port on which IP on the other side. No effort is made to monitor the communication other than allowing some IP/port/destination/origin-combinations and blocking everything else.

Stateful inspection is different: packets are interpreted and their content is checked. Packets (or, rather, whole connections) are allowed/disallowed based on these checks. This needs a lot more computing and is a lot more intrusive than packet filtering and therefore real-world firewalls are usually a combination of both packet filters and some stateful inspection.

I hope this helps.

bakunin
 

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stone(1)						      General Commands Manual							  stone(1)

NAME
stone - a simple TCP/IP packet repeater SYNOPSYS
stone [-d] [-n] [-u max] [-f n] [-l] [-z SSL] st [-- st] ... OPTIONS
-d Increase the debug level. -z SSL encryption. -n IP addresses and service port numbers are shown instead of host names and service names. -u max max is integer. The program will memorize max sources simultaneously where UDP packets are sent. -f n n is integer. The program will spawn n child processes. -l Sends error messages to the syslog instead of stderr. st is one of the followings; Multiple st can be designated, separated by --. (1) host:port sport [xhost ...] (2) host:port shost:sport [xhost ...] (3) display [xhost ...] (4) proxy sport [xhost ...] (5) host:port/http request [hosts ...] (6) host:port/proxy header [hosts...] The program repeats the connection on port sport to the other machine host port port. If the machine, on which the program runs, has two or more interfaces, type (2) can be used to repeat the connection on the specified interface shost. display [xhost ...] Abbreviating notation. The program repeats the connection on display number display to the X server designated by the environment variable DISPLAY. proxy sport [xhost ...] Http Proxy. Specify the machine, on which the program runs, and port sport in the http proxy settings of your WWW browser. host:port/http request [hosts ...] Repeats packets over http request. request is the request specified in HTTP 1.0. host:port/proxy header [hosts...] host:port/proxy header [hosts...] Type (6) repeats http request with header in the top of request headers. xhost Only machines xhost can connect to the program. xhost/mask Only machines on specified networks are permitted to connect to the program. In the case of class C network 192.168.1.0, for exam- ple, use 192.168.1.0/255.255.255.0. sport/udp Repeats UDP packets instead of TCP packets. port/ssl Repeats packets with encryption. sport/ssl Repeats packets with decryption. sport/http Repeats packets over http. DESCRIPTION
Stone is a TCP/IP packet repeater in the application layer. It repeats TCP and UDP packets from inside to outside of a firewall, or from outside to inside. Stone has following features: 1. Stone supports Win32. Formerly, UNIX machines are used as firewalls, but recently WindowsNT machines are used, too. You can easily run Stone on WindowsNT and Windows95. Of course, available on Linux, FreeBSD, BSD/OS, SunOS, Solaris, HP-UX and so on. 2. Simple. Stone's source code is only 2000 lines long (written in C language), so you can minimize the risk of security holes. 3. Stone supports SSLeay. Using SSLeay developed by Eric Young, Stone can encrypt/decrypt packets. 4. Stone is a http proxy. Stone can also be a tiny http proxy. EXAMPLES
outer: a machine in the outside of the firewall inner: a machine in the inside of the firewall fwall: the firewall on which the stone is executed stone 7 outer Repeats the X protocol to the machine designated by the environmental variable DISPLAY. Run X clients under DISPLAY=inner:7 on outer. stone outer:telnet 10023 Repeats the telnet protocol to outer. Run telnet fwall 10023 on inner. stone outer:domain/udp domain/udp Repeats the DNS query to outer. Run nslookup - fwall on inner. stone outer:ntp/udp ntp/udp Repeats the NTP to outer. Run ntpdate fwall on inner. stone localhost:http 443/ssl Make WWW server that supports https. Access https://fwall/ using a WWW browser. stone localhost:telnet 10023/ssl Make telnet server that supports SSL. Run SSLtelnet -z ssl fwall 10023 on inner. stone proxy 8080 http proxy. Where fwall is a http proxy (port 8080): stone fwall:8080/http 10023 'POST http://outer:8023 HTTP/1.0' stone localhost:telnet 8023/http Run stones on inner and outer respectively. Repeats packets over http. stone fwall:8080/proxy 9080 'Proxy-Authorization: Basic c2VuZ29rdTpoaXJvYWtp' for browser that does not support proxy authorization. COPYRIGHT
All rights about this program stone are reserved by the original author, Hiroaki Sengoku. The program is free software; you can redis- tribute it and/or modify it under the terms of the GNU General Public License (GPL). NO WARRANTY
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY. AUTHOR
Hiroaki Sengoku sengoku@gcd.org http://www.gcd.org/sengoku/ Version 2.0 stone(1)
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