SYNOPSIS

Defaults:

• DEFAULT_INTERFACE_POLICY="DROP"
• DEFAULT_ROUTER_POLICY="RETURN"
• UNMATCHED_INPUT_POLICY="DROP"
• UNMATCHED_OUTPUT_POLICY="DROP"
• UNMATCHED_FORWARD_POLICY="DROP"
• FIREHOL_INPUT_ACTIVATION_POLICY="ACCEPT"
• FIREHOL_OUTPUT_ACTIVATION_POLICY="ACCEPT"
• FIREHOL_FORWARD_ACTIVATION_POLICY="ACCEPT"
• FIREHOL_LOG_MODE="LOG"
• FIREHOL_LOG_LEVEL=see notes
• FIREHOL_LOG_OPTIONS="--log-level warning"
• FIREHOL_LOG_FREQUENCY="1/second"
• FIREHOL_LOG_BURST="5"
• FIREHOL_LOG_PREFIX=""
• FIREHOL_DROP_INVALID="0"
• DEFAULT_CLIENT_PORTS="1000:65535"
• FIREHOL_NAT="0"
• FIREHOL_ROUTING="0"
• FIREHOL_AUTOSAVE=see notes
• FIREHOL_AUTOSAVE6=see notes
• FIREHOL_LOAD_KERNEL_MODULES="1"
• FIREHOL_TRUST_LOOPBACK="1"
• FIREHOL_DROP_ORPHAN_TCP_ACK_FIN="0"
• FIREHOL_DEBUGGING=""
• WAIT_FOR_IFACE=""

DESCRIPTION

There are a number of variables that control the behaviour of FireHOL.

All variables may be set in the main FireHOL configuration file /etc/firehol/firehol.conf.

Variables which affect the runtime but not the created firewall may also be set as environment variables before running firehol(1). These can change the default values but will be overwritten by values set in the configuration file. If a variable can be set by an environment variable it is specified below.

FireHOL also sets some variables before processing the configuration file which you can use as part of your configuration. These are described in firehol.conf(5).

VARIABLES

DEFAULT_INTERFACE_POLICY

This variable controls the default action to be taken on traffic not matched by any rule within an interface. It can be overridden using firehol-policy(5).

Packets that reach the end of an interface without an action of return or accept are logged. You can control the frequency of this logging by altering FIREHOL_LOG_FREQUENCY.

Example:

DEFAULT_INTERFACE_POLICY="REJECT"

DEFAULT_ROUTER_POLICY

This variable controls the default action to be taken on traffic not matched by any rule within a router. It can be overridden using firehol-policy(5).

Packets that reach the end of a router without an action of return or accept are logged. You can control the frequency of this logging by altering FIREHOL_LOG_FREQUENCY.

Example:

DEFAULT_ROUTER_POLICY="REJECT"

UNMATCHED_{INPUT|OUTPUT|FORWARD}_POLICY

These variables control the default action to be taken on traffic not matched by any interface or router definition that was incoming, outgoing or for forwarding respectively. Any supported value from firehol-actions(5) may be set.

All packets that reach the end of a chain are logged, regardless of these settings. You can control the frequency of this logging by altering FIREHOL_LOG_FREQUENCY.

Example:

UNMATCHED_INPUT_POLICY="REJECT"
UNMATCHED_OUTPUT_POLICY="REJECT"
UNMATCHED_FORWARD_POLICY="REJECT"

FIREHOL_{INPUT|OUTPUT|FORWARD}_ACTIVATION_POLICY

These variables control the default action to be taken on traffic during firewall activation for incoming, outgoing and forwarding respectively. Acceptable values are ACCEPT, DROP and REJECT. They may be set as environment variables.

FireHOL defaults all values to ACCEPT so that your communications continue to work uninterrupted.

If you wish to prevent connections whilst the new firewall is activating, set these values to DROP. This is important to do if you are using all or any to match traffic; connections established during activation will continue even if they would not be allowed once the firewall is established.

Example:

FIREHOL_INPUT_ACTIVATION_POLICY="DROP"
FIREHOL_OUTPUT_ACTIVATION_POLICY="DROP"
FIREHOL_FORWARD_ACTIVATION_POLICY="DROP"

FIREHOL_LOG_MODE

This variable controls method that FireHOL uses for logging.

Acceptable values are LOG (normal syslog) and ULOG (netfilter ulogd). When ULOG is selected, FIREHOL_LOG_LEVEL is ignored.

Example:

FIREHOL_LOG_MODE="ULOG"

To see the available options run: /sbin/iptables -j LOG --help or /sbin/iptables -j ULOG --help

FIREHOL_LOG_LEVEL

This variable controls the level at which events will be logged to syslog.

To avoid packet logs appearing on your console you should ensure klogd only logs traffic that is more important than that produced by FireHOL.

Use the following option to choose an iptables(8) log level (alpha or numeric) which is higher than the -c of klogd.

iptables/klogd levels

iptables	klogd	description
emerg (0)	0	system is unusable
alert (1)	1	action must be taken immediately
crit (2)	2	critical conditions
error (3)	3	error conditions
warning (4)	4	warning conditions
notice (5)	5	normal but significant condition
info (6)	6	informational
debug (7)	7	debug-level messages

Note

The default for klogd is generally to log everything (7 and lower) and the default level for iptables(4) is to log as warning (4).

FIREHOL_LOG_OPTIONS

This variable controls the way in which events will be logged to syslog.

Example:

FIREHOL_LOG_OPTIONS="--log-level info \
                     --log-tcp-options --log-ip-options"

To see the available options run: /sbin/iptables -j LOG --help

FIREHOL_LOG_FREQUENCY; FIREHOL_LOG_BURST

These variables control the frequency that each logging rule will write events to syslog. FIREHOL_LOG_FREQUENCY is set to the maximum average frequency and FIREHOL_LOG_BURST specifies the maximum initial number.

Example:

FIREHOL_LOG_FREQUENCY="30/minute"
FIREHOL_LOG_BURST="2"

To see the available options run: /sbin/iptables -m limit --help

FIREHOL_LOG_PREFIX

This value is added to the contents of each logged line for easy detection of FireHOL lines in the system logs. By default it is empty.

Example:

FIREHOL_LOG_PREFIX="FIREHOL:"

FIREHOL_DROP_INVALID

If set to 1, this variable causes FireHOL to drop all packets matched as INVALID in the iptables(8) connection tracker.

You may be better off using firehol-protection(5) to control matching of INVALID packets and others on a per-interface and per-router basis.

Note

Care must be taken on IPv6 interfaces, since ICMPv6 packets such as Neighbour Discovery are not tracked, meaning they are marked as INVALID.

Example:

FIREHOL_DROP_INVALID="1"

DEFAULT_CLIENT_PORTS

This variable controls the port range that is used when a remote client is specified. For clients on the local host, FireHOL finds the exact client ports by querying the kernel options.

Example:

DEFAULT_CLIENT_PORTS="0:65535"

FIREHOL_NAT

If set to 1, this variable causes FireHOL to load the NAT kernel modules. If you make use of the NAT helper commands, the variable will be set to 1 automatically. It may be set as an environment variable.

Example:

FIREHOL_NAT="1"

FIREHOL_ROUTING

If set to 1, this variable causes FireHOL to enable routing in the kernel. If you make use of router definitions or certain helper commands the variable will be set to 1 automatically. It may be set as an environment variable.

Example:

FIREHOL_ROUTING="1"

FIREHOL_AUTOSAVE; FIREHOL_AUTOSAVE6

These variables specify the file of IPv4/IPv6 rules that will be created when firehol(1) is called with the save argument. It may be set as an environment variable.

If the variable is not set, a system-specific value is used which was defined at configure-time. If no value was chosen then the save fails.

Example:

FIREHOL_AUTOSAVE="/tmp/firehol-saved-ipv4.txt"
FIREHOL_AUTOSAVE6="/tmp/firehol-saved-ipv6.txt"

FIREHOL_LOAD_KERNEL_MODULES

If set to 0, this variable forces FireHOL to not load any kernel modules. It is needed only if the kernel has modules statically included and in the rare event that FireHOL cannot access the kernel configuration. It may be set as an environment variable.

Example:

FIREHOL_LOAD_KERNEL_MODULES="0"

FIREHOL_TRUST_LOOPBACK

If set to 0, the loopback device "lo" will not be trusted and you can write standard firewall rules for it.

Warning

If you do not set up appropriate rules, local processes will not be able to communicate with each other which can result in serious breakages.

By default "lo" is trusted and all INPUT and OUTPUT traffic is accepted (forwarding is not included).

Example:

FIREHOL_TRUST_LOOPBACK="0"

FIREHOL_DROP_ORPHAN_TCP_ACK_FIN

If set to 1, FireHOL will drop all TCP connections with ACK FIN set without logging them.

In busy environments the iptables(8) connection tracker removes connection tracking list entries as soon as it receives a FIN. This makes the ACK FIN appear as an invalid packet which will normally be logged by FireHOL.

Example:

FIREHOL_DROP_ORPHAN_TCP_ACK_FIN="1"

FIREHOL_DEBUGGING

If set to a non-empty value, switches on debug output so that it is possible to see what processing FireHOL is doing.

Note

This variable can only be set as an environment variable, since it is processed before any configuration files are read.

Example:

FIREHOL_DEBUGGING="Y"

WAIT_FOR_IFACE

If set to the name of a network device (e.g. eth0), FireHOL will wait until the device is up (or until 60 seconds have elapsed) before continuing.

Note

This variable can only be set as an environment variable, since it determines when the main configuration file will be processed.

A device does not need to be up in order to have firewall rules created for it, so this option should only be used if you have a specific need to wait (e.g. the network must be queried to determine the hosts or ports which will be firewalled).

Example:

WAIT_FOR_IFACE="eth0"

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