firehol - An easy to use but powerful iptables stateful firewall

firehol start|try|stop|restart|condrestart|status|panic|save|debug|helpme

firehol configfile [start|debug|try]

firehol nothing

firehol is an iptables firewall generator producing stateful iptables packet filtering firewalls, on Linux hosts and routers with any number of network interfaces, any number of routes, any number of services served, any number of complexity between variations of the services (including positive and negative expressions).

firehol is a language to express firewalling rules, not just a script that produces some kind of a firewall.

The goals of firehol are:

• Being as easy as possible

Independently of the security skills he/she has, firehol allows to create and understand complex firewalls in just a few seconds. The configuration files are very easy to type and read.

• Being as secure as possible.

By allowing explicitly only the wanted traffic to flow firehol secures your system. firehol produces stateful rules for any service or protocol, in both directions of the firewall.

• Being as open as possible.

Althoug firehol is pre-configured for a large number of services, you can configure any service you like and firehol will turn it into a client, a server, or a router.

• Being as flexible as possible.

firehol can be used by end users and guru administrators requiring extremely complex firewalls. firehol configuration files are BASH scripts; you can write in them anything BASH accepts, including variables, pipes, loops, conditions, calls to external programs, run other BASH scripts with firehol directives in them, etc.

• Being as simple as possible.

firehol is easy to install on any modern Linux system; only one file is required, no compilations involved.

start

Activates the firewall configuration. The configuration is expected to be found in /etc/firehol.conf.

try

Activates the firewall, but waits until the user types the word commit. If this word is not typed within 30 seconds, the previous firewall is restored.

stop

Stops a running iptables firewall by running CW/etc/init.d/iptables stop. This will allow all traffic to pass unchecked.

restart

This is an alias for start and is given for compatibility with /etc/init.d/iptables.

condrestart

Starts the firehol firewall only if it is not already active. It does not detect a modified configuration file, only verifies that firehol has been started in the past and not stopped yet.

status

Shows the running firewall, as in CW/sbin/iptables -nxvL | less

panic

It removes all rules from the running firewall and then it DROPs all traffic on all iptables tables (mangle, nat, filter) and pre-defined chains (PREROUTING, INPUT, FORWARD, OUTPUT, POSTROUTING), thus blocking all IP communication. DROPing is not done by changing the default policy to DROP, but by adding just one rule per table/chain to drop all traffic, because the default iptables scripts supplied by many systems (including RedHat 8) do not reset all the chains to ACCEPT when starting (firehol resets them correctly). When activating panic mode, firehol checks for the existance of the SSH_CLIENT shell environment variable (set by SSH). If it find this, then panic mode will allow the established SSH connection specified in this variable to operate. Notice that in order for this to work, you should have su without the minus (-) sign, since su - overwrites the shell variables and therefore the SSH_CLIENT variable is lost. Alternativelly, after the panic argument you can specify an IP address in which case all established connections between this IP address and the host in panic will be allowed.

save

Start the firewall and then save it using /sbin/iptables-save to /etc/sysconfig/iptables. Since v1.64, this is not implemented using CW/etc/init.d/iptables save because there is a bug in some versions of iptables-save that save invalid commands (CW! --uid-owner A is saved as CW--uid-owner !A) which cannot be restored. firehol fixes this problem (by saving it, and then replacing CW--uid-owner ! with CW! --uid-owner). Note that not all firehol firewalls will work if restored with: CW/etc/init.d/iptables start because FireHOL handles kernel modules and might have queried RPC servers (used by the NFS service) before starting the firewall. Also, firehol automatically checks current kernel configuration for client ports range. If you restore a firewall using the iptables service your firewall may not work as expected.

debug

Parses the configuration file but instead of activating it, it shows the generated iptables statements.

explain

Enters an interactive mode where it accepts normal configuration commands and presents the generated iptables commands for each of them, together with some reasoning for its purpose. Additionally, it automatically generates a configuration script based on the successfull commands given. When in directive mode, firehol has the following special commands:

• help

Present some help

• show

Present the generated firehol configuration

• quit

Exit interactive mode and quit firehol

helpme

Tries to guess the firehol configuration needed for the current machine. firehol will not stop or alter the running firewall. The configuration file is given in the standard output of firehol, thus

 /etc/init.d/firehol helpme >/tmp/firehol.conf

will produce the output in /tmp/firehol.conf. The generated firehol configuration should and must be edited before used on your systems. You are required to take many decisions and the comments of the generated file will instruct you for many of them.

configfile

A different configuration file. If no other argument is given, the configuration file will be tried (default = try). Otherwise the argument next to the filename can be one of start, debug, try.

nothing

Presents help about firehol usage.

/etc/firehol.conf

firehol written by Costa Tsaousis <costa@tsaousis.gr>.

Man page written by Marc Brockschmidt <marc@marcbrockschmidt.de>.

firehol.conf(5), iptables(8), bash(1)