Lots of fuzz in the media about Suricata’s performance versus Snort yesterday. Some claiming Suricata is much faster, others claiming Snort is much faster.
At this point I really don’t care much. What the Suricata development by the OISF has shown in my opinion is that we’ve managed to create a very promising new Open Source project out here. In little over a year, funded for about $600k by the US government and with heavy (and growing) industry support, we’ve produced a new IDS/IPS engine mostly compatible with Snort but build on a all new code base an incorporating some very interesting fresh ideas. We’re already seeing a community form around our project with a lot of support from that new community.
So about this performance fuzz. Who to believe? Is Suricata faster than Snort? Yes, no, ehhh, depends on how you look at it. Is Suricata faster than Snort on a single core cycle for cycle, tick for tick? No. It’s pretty clear we aren’t, I didn’t expect us to be either. But we scale. We’ve had reports of running on a 32 core box and scaling to use all cores. There Suricata is much faster. Like Martin Roesch wrote on the VRT blog one can set up Snort on a box to one have instance of Snort per core (or multiple per core). This is in fact the way many appliance builders get to high speeds with it. While this may be feasible for appliance builders, admins we talked to that run their own IDS/IPS think it’s a management nightmare.
As we’re a new project with a fresh codebase, there is going to be a lot of low hanging fruit in performance optimizations. I’ll give an example here. On a test pcap, with a reduced ruleset (about 10k rules), Suricata took about 400s to inspect. Then with a bigger ruleset (about 14k rules), it suddenly took 1600s! After a little bit of cache profiling it turned out that the part of the engine where the address part of a signature was inspected was horribly cache inefficient. In less than an afternoon I rewrote it to be more efficient. Result, the same test now completes in under 600s. This code is in the current git master and will be in 1.0.1.
My point here being that there will be lots of room for optimizations, and not just minor stuff. So far we’ve mostly focused on being accurate (we still have work to do here) and having the algorithms be correct. Hardly any tuning has been done. In our last OISF meeting we’ve gotten a few very interesting help offers for serious performance testing and tuning on some really big boxes, state of the art CUDA hardware, 10GBit labs, etc. So I expect a lot of progress in the months to follow.
It’s clear that we have work to do. What I’m really excited about is how fast that work is progressing, how much help we’re getting both from our brand new community and the industry, and the openness of our development process.
On a final note, during the development of this project we’ve found a lot of bugs and issues in other tools. Will Metcalf, who runs our QA, has been reporting many issues in Snort and VRT sigs to Sourcefire, in Emerging Threats sigs to the ET community. We’ve found bugs in other tools as well, for example in a neat library called libcap-ng. So everyone benefits from our work! 
