A while ago I wrote about porting Snort_inline to 18.104.22.168. That worked well, however we are still trying to resolve some issues. Especially in stickydrop, that is just broken right now. Also, SourceFire released 22.214.171.124 last week, so we need to update to that too.
First however, I will be traveling to California this week. I will be meeting Will there, so I’ll try to get him to fix that damn code 😉
Every few weeks the same question comes up: what is the difference between Snort in inline mode and Snort_inline. This makes sense, because the Snort_inline documentation and website fail to explain it. In this post I will try to highlight the main differences. In general I can say that we try to develop Snort_inline as a patchset on top of Snort. Snort_inline is focused at improving the inline part of Snort. Originally of course, Snort’s inline capabilities were developed in the Snort_inline project. With Snort 2.3.0RC1 they were merged into mainline Snort.
We did a number of things to make Snort_inline a little more convenient for inline users.
- inline is enabled by default in ./configure
- we got rid of libnet 1.0.2a, switched to libdnet 1.1 instead
- a snort_inline specific manual page was added, as well as some extra docs
- a example configuration file for inline use is supplied
- we support Linux’ new queue’ing mechanism called nfqueue. This was contributed by Nitro Security. Nfqueue supports running multiple copies of Snort_inline to take advantage of SMP and reduce risk of denial of service when Snort_inline should crash.
- stickydrop preprocessor enables you to add options to the rules to block an ipaddress for a configurable amount of time
- bait-and-switch preprocessor (Linux only) allows you to redirect traffic from a host to a honeypot based on the rules
- clamav preprocessor is included (you still need to pass –enable-clamav to ./configure)
- reinject action for FreeBSD: reinjects an accepted packet into the ipfw list at a specific rule number
Improved for inline use
- reject action can send RST packets to both source and destination
- stream4 can drop attacks detected in the reassembled stream. It also enforces the TCP window. It implements a number of ideas from Vern Paxson on TCP reassembly, such as a limit on the number of out of order packets and bytes that are accepted in a stream.
- some fixes for FreeBSD
As the list shows, if you are interested in Snort running inline, using Snort_inline might be a better choice for you!