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

apf

APF(1)							      General Commands Manual							    APF(1)

NAME

       apf - easy iptables based firewall system

SYNOPSIS

       apf

DESCRIPTION

       This  manual page documents briefly the apf command.  This manual page was written for the Debian distribution because the original program
       does not have a manual page.

       Advanced Policy Firewall (APF) is an iptables (netfilter) based firewall system designed around the essential  needs  of  today's  Internet
       deployed  servers  and the unique needs of custom deployed Linux installations. The configuration of APF is designed to be very informative
       and present the user with an easy to follow process, from top to bottom of the configuration file. The management of APF  on  a	day-to-day
       basis  is  conducted from the command line with the 'apf' command, which includes detailed usage information and all the features one would
       expect from a current and forward thinking firewall solution.

OPTIONS

       apf follow the usual GNU command line syntax, with long options starting with two dashes (`-').	A summary of options is included below.

       -s|--start
	      load all firewall rules

       -r|--restart
	      stop (flush) & reload firewall rules

       -l|--list
	      list all firewall rules

       -t|--status
	      output firewall status log

       -e|--refresh
	      refresh & resolve dns names in trust rules

       -a <HOST CMT|--allow <HOST COMMENT>
	      add host (IP/FQDN) to allow_hosts.rules and immediately load new rule into firewall

       -d <HOST CMT|--deny <HOST COMMENT>
	      add host (IP/FQDN) to deny_hosts.rules and immediately load new rule into firewall

       -u <HOST>|--remove <HOST>
	      remove host from [glob]*_hosts.rules and immediately remove rule from firewall

       -o|--ovars
	      output all configuration options

COPYRIGHT

       Copyright (C) 1999-2007, R-fx Networks <proj@r-fx.org>
       Copyright (C) 2007, Ryan MacDonald <ryan@r-fx.org> This program may be freely redistributed under the terms of the GNU GPL

       This manual page was written by Giuseppe Iuculano <giuseppe@iuculano.it>, for the Debian project (but may be used by others).

								  August 17, 2008							    APF(1)