Creator: Jed Haile <jed@grep.net>Current Maintainer: Rob McMillen <rvmcmil@cablespeed.com>                    William Metcalf <william.metcalf@gmail.com>                    Victor Julien <victor@nk.nl>Snort-Inline takes packets from iptables instead of libpcap.  It then uses new rule types to help iptables make pass or drop decisions based on snort rules.  In order for snort_inline to work properly, you must download and compilethe iptables code to include "make install-devel" (www.iptables.org).  This will install the libipq library that allows snort_inline to interface with iptables.  Also, you must build and install LibNet, which is availablefrom www.packetfactory.net.The snort_inline FAQ can be found at http://snort-inline.com/FAQ.html.NEW RULE TYPES AND WHAT THEY DO:drop - The drop rule type will tell iptables to drop the packet and log it        via usual snort means.reject - The reject rule type will tell iptables to drop the packet, log it          via usual snort means, and send a TCP reset if the protocol is          TCP or an icmp port unreachable if the protocol is UDP.sdrop - The sdrop rule type will tell iptables to drop the packet.  Nothing        is logged.RESETS: We now have two options on how to send out resets. We can still usea RAW socket which is the default behavior for snort_inline in which casewe need to have an interface that has an ip assigned. If there is not aninterface with an ip address assigned with access to the source of the packet,the packet will be logged and the reset packet will never make it onto the network.We can also now perform resets via a physical device when using iptables.We take the indev name from ip_queue and use this as the interface on whichto send resets. We no longer need a ip loaded on the bridge, and can remainpretty stealthy as the config layer2_resets in snort_inline.conf takes a sourcemac address which we substitue for the mac of the bridge. For example:CONFIG OPTIONSconfig layer2resetstells snort_inline to use layer2 rests and uses the mac address of the bridge as the source mac in the packet.config layer2resets: 00:06:76:DD:5F:E3  will tell snort_inline to use layer2 resets and uses the src mac of 00:06:76:DD:5F:E3 in the rest packet. STREAM4 OPTIONSThere are two additional stream4 options:inline_state (no args)    This option causes snort to drop TCP packets that are not associated with     an existing TCP session, and is not a valid TCP initiator.midstream_drop_alerts (no args)    By default, when running in inline mode, snort will silently drop any    packets that were picked up in midstream and would have caused an alert    to be generated, if not for the 'flow: established' option.  This is to    mitigate stick/snot type attacks when the user hasn't enabled     inline_state.  If the user wants to see the alerts that are silently    dropped, then enable this keyword.  Note that by enabling this keyword,    the user has opened themselves up to stick/snot type attacks. ALSO...Additionally, Jed's content replace code allows you to modify packetsbefore they leave the network.  For example:alert tcp any any <> any 80 (msg: "tcp replace"; content:"GET"; replace:"BET";)alert udp any any <> any 53 (msg: "udp replace"; \    content: "yahoo"; replace: "xxxxx";)these rules will comb tcp port 80 traffic looking for GET, and udp port 53 traffic looking for yahoo.  Once they are found, they are replaced with BET and xxxxx, respectively.  The only catch is that the replace must be the same length as the content.RULE APPLICATION ORDER:The current Rule application order: 	->activation->dynamic->drop->sdrop->reject->alert->pass->logThis will ensure that a drop rule has precedence over an alert or log rule.Also, the -o flag now changes the rule application order to:	->activation->dynamic->pass->drop->sdrop->reject->alert->logINSTALL./configure --enable-inlinemakemake installDROP RULESMike Clark <mike@honeynet.org> has taken the time and energy to go throughthe snort ruleset to identify and consolidate rules that would meet thedrop criteria.  These rules are located in the rules directory in drop.rules, and should be considered "alpha".  There is also a sample drop.conf file located in the etc directory of the snort_inline.tgz.  The latest and greatest set of drop rules can always be found at:http://www.honeynet.org/papers/honeynet/tools/Additionally, we have included a convert.sh script in the etc/ directorythat will convert all alert rules to drop rules.  All you have to do is copy it to the location of your snort rules and run it.  It will convertall alert rules to drop rules; change HOME_NET to HONEYNET; and reversethe flow of the rules.  Why reverse the flow of the rules?  Because theoriginal purpose of snort_inline is to control a compromised network;therefore, we need to drop packets leaving the Honeynet not entering it.HONEYNET SNORT_INLINE TOOLKITThis is a statically compiled snort_inline binary put together by theHoneynet Project for the Linux Operating System.  It comes with a setof drop.rules, the snort_inline binary, a snort-inline rotation shellscript, and a good README.  It can be found at:http://www.honeynet.org/papers/honeynet/tools/RUNFirst, you need to ensure that the ip_queue module is loaded.  Then,you need to send traffic to snort_inline using the QUEUE target.  Forexample,iptables -A OUTPUT -p tcp --dport 80 -j QUEUEsends all tcp traffic leaving the firewall going to port 80 to the QUEUEtarget.  This is what sends the packet from kernel space to user space (snort_inline).  A quick way to get all outbound traffic going to theQUEUE is to use the rc.firewall script created and maintained by the Honeynet Project (http://www.honeynet.org/papers/honeynet/tools/)This script is well documented and allows you to direct packetsto snort_inline by simply changing the QUEUE variable to yes.Finally, start snort_inline.snort_inline -QDc ../etc/drop.conf -l /var/log/snort-Q => get packets from iptables.-D => run in daemon mode.  pid in /var/run/snort_inline.pid-c => read the following configuration file.-l => log to the following directory.Ideally, snort_inline will be run using only its own drop.rules.  Ifyou want to use Snort for just alerting, a separate process should berunning with its own ruleset.TROUBLESHOOTINGIf you execute snort_inline, and you see something like this:Initializing Output Plugins!Reading from iptablesLog directory = /var/log/snortInitializing Inline modeInlineInit: : Failed to send netlink message: Connection refusedmore than likely, the ip_queue module is not loaded or ip_queue support is not compiled into your kernel.  Either recompileyour kernel to support ip_queue, or load the module.The ip_queue module is loaded by executing:insmod ip_queueAlso, if you want to ensure snort_inline is getting packets, you can start it in the following manner:snort_inline -Qvc <configuration file>This will display the header of every packet that snort_inline sees.