How to check the IP:PORT firewall uses? Post: 303004043

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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

09-25-2017

Registered User

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

bakunin

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LEARN ABOUT DEBIAN

arno-iptables-firewall

ARNO-IPTABLES-FIREWALL(8)												 ARNO-IPTABLES-FIREWALL(8)

NAME

       arno-iptables-firewall - Single- & multi-homed firewall script with DSL/ADSL support.

SYNOPSIS

       /etc/init.d/arno-iptables-firewall [start|stop|status|force-reload|restart]

DESCRIPTION

       arno-iptables-firewall  is  an  iptables configuration script with support for both IPv4 & IPv6.  While it is extremely easy to use one can
       nevertheless use it in quite complicated environments.

       All available options are explained in the extensively documented configuration file.

       The external interface of the system needs to be set up properly in the firewalls configuration file (EXT_IF).  The default behavior of the
       firewall is to deny all incoming connections.

       For  additional	requirements not covered by the configuration file custom iptables rules can be placed in /etc/arno-iptables-firewall/cus-
       tom-rules.  This file is automatically parsed by the service script.

       See the README file (eg. in /usr/(local/)share/doc/arno-iptables-firewall) for an example how to manage logging of firewall events  through
       syslogd.

       The arno-fwfilter script can be used to make the firewall logs more readable for humans (see manpage).

       Several plugins for the firewall script are available online. Plugins can be downloaded from http://rocky.eld.leidenuniv.nl/ Please see the
       README file for more information.

FILES

       /etc/init.d/arno-iptables-firewall	       system service script
       /etc/arno-iptables-firewall/firewall.conf       firewall configuration
       /etc/arno-iptables-firewall/conf.d/	       firewall configuration directory
       /etc/arno-iptables-firewall/custom-rules        custom iptables rules
       /etc/arno-iptables-firewall/blocked-hosts       host blacklist
       /etc/arno-iptables-firewall/mac-addresses       mac filter list

       Please note, that the last two files do exist in the initial configuration and their use is disabled  in  /etc/arno-iptables-firewall/fire-
       wall.conf

SEE ALSO

       iptables(8), arno-fwfilter(1), syslog.conf(5)

       The http://rocky.eld.leidenuniv.nl/ web site.

AUTHOR

       arno-iptables-firewall was written by Arno van Amersfoort <arnova@rocky.eld.leidenuniv.nl>.

       This manual page was written by Michael Hanke <michael.hanke@gmail.com>, for the Debian project (but may be used by others).

Michael Hanke							  March 14, 2012					 ARNO-IPTABLES-FIREWALL(8)