![]() You must change the action of rules you wish to block traffic to be either DROP or REJECT. However, Inline IPS Mode is quite different! Because the default action of all rules from the rule vendors is ALERT, if you enable Inline IPS Mode but don't change the rule actions, you will get no blocks. With Legacy Mode blocking, once you enable "Block Offenders" there is nothing else to do. Key and Important Difference Between Inline Mode and Legacy Mode: REJECT rules drop the packet but send either a RST (for TCP traffic) or a "Destination port unreachable" (for UDP or ICMP traffic) to the originating host. DROP rules drop the packet without any indication to the sender. You do this by changing the rule's action from the default ALERT to either DROP or REJECT. The major advantage offered by this new operating mode is the ability to now select which rules alert but don't block, and which rules alert and block. ![]() A dropped packet is the same as "blocked". Snort can then either allow the packet to pass, or it can drop it. In this manner, all traffic flowing to and from the physical interface and the operating system must pass through Snort. #NETMAP SUPPORT DRIVER#Instead, it uses the netmap module within the DAQ library to create a netmap pipe between a physical NIC driver and the pfSense operating system network stack. The new Inline IPS Mode dispenses with the custom output plugin used by the Legacy Mode blocking. It's either all block or all alert (blocking off). The downside of this approach is that the admin can't choose rules to just alert and other rules to block. A hidden firewall rule (hidden from the GUI but visible if you view the contents of the /tmp/bug file) then blocks any IP address entered into the snort2c table. This table is created by pfSense at boot-up. The custom blocking plugin extracts the IP addresses from the alerting packet and then, after screening them through a Pass List filter, will make a FreeBSD system call to place the offending IP addresses in a pf (packet filter) table called snort2c. This custom plugin receives a copy of every single alert generated by a Snort rule. Snort on pfSense uses a custom output plugin to implement the Legacy Mode blocking. To contrast the difference, let's briefly dive into the details of how Snort works on pfSense. This mode operates quite differently from the original Legacy Mode blocking. The Snort 4.0 package offers a new mode of operation called Inline IPS Mode. If your NIC driver is not from one of these families, netmap and Inline IPS Mode is not going to work properly, if it works at all. Only the following NIC families currently have netmap support in FreeBSD and hence pfSense: em, igb, ixgb, ixl, lem, re or cxgbe. ![]() The new Inline IPS Mode of Snort will only work on interfaces running on a supported network interface card (NIC). Snort Package 4.0 Inline IPS Mode Configuration ![]()
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