Command Line Options for fwsnort

There are many command-line options for fwsnort that you can use to influence its execution, and we'll cover some of the more commonly used ones here. (You'll find an exhaustive treatment of all command-line arguments in the fwsnort(8) man page.)

--ipt-drop This option instructs fwsnort to drop packets before they are forwarded to their intended target, in addition to logging them. (By default, fwsnort only logs malicious packets.) This grants fwsnort the authority to actively respond to network attacks.

3 This makes it possible to execute the script multiple times and maintain a clean interface with an existing iptables policy since only one fwsnort jump rule can exist for each built-in chain. Versions of fwsnort prior to 1.0 had a bug where additional jump rules were added if the script was executed multiple times.

--ipt-reject This option instructs fwsnort to build an iptables policy that utilizes the REJECT target to tear down malicious TCP connections with TCP Reset packets, and to respond against malicious UDP traffic with an ICMP Port Unreachable message.

--snort-conf path This option instructs fwsnort to read variables such as HOME_NET, EXTERNAL_NET, HTTP_SERVERS, and so on directly from an existing Snort configuration file (usually located at /etc/snort/snort.conf). There is nothing to prevent Snort and fwsnort from running on the same system. This remains true even when Snort is running in inline mode, because fwsnort rules are sectioned off within their own chains; packets can be jumped to these chains before hitting a QUEUE rule within the iptables policy.

--snort-sid sids This option allows the translation efforts of fwsnort to be restricted to a specific Snort ID or a list of Snort IDs. This is most useful when a new vulnerability is announced in a piece of software that is protected by an iptables firewall and a new signature is released by the Snort community to detect an attack that exploits this vulnerability. By using fwsnort with the --snort-sid option, we can quickly deploy a new policy to log and/or drop malicious packets that are associated with this new attack.

--include-type type This option instructs fwsnort to translate only Snort rules that are contained within a single rules file. For example, to translate the rules from the backdoor.rules file, one would use --include-type backdoor on the fwsnort command line. A comma-separated list of types is also supported, such as --include-type ftp,mysql.

--ipt-list This option displays all active rules in the various fwsnort chains. These include FWSNORT_INPUT, FWSNORT_INPUT_ESTAB, FWSNORT_OUTPUT, FWSNORT_OUTPUT_ESTAB, FWSNORT_FORWARD, and FWSNORT_FORWARD_ESTAB.

--ipt-flush This option flushes all active rules in the fwsnort chains. This is useful for quickly removing fwsnort rules without removing other iptables rules associated with an existing policy.

--no-addresses This option forces fwsnort to not reference IP addresses associated with any interfaces on the firewall system. This option is most useful if fwsnort is deployed on a bridging firewall that has no IP addresses assigned to its interfaces.

--no-ipt-sync This option instructs fwsnort to disable all compatibility checks that are normally run against the local iptables policy. The resulting fwsnort policy will not skip any rules that detect traffic that the firewall is configured to not accept in the first place.

--restrict-intf intf This option restricts fwsnort rules to the specified interface (or interfaces). By default, fwsnort does not inspect traffic over the loopback interface but inspects traffic on all other interfaces. To have fwsnort inspect traffic over, say, the eth0 and eth1 interfaces only, you would use --restrict-intf eth0,eth1.

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