[Oisf-users] Making Suricata Alert Per Matching Packet

Cooper F. Nelson cnelson at ucsd.edu
Mon Apr 11 21:59:59 UTC 2016

Well, first of all IP-only rules usually have a threshold set as most
folks don't want them alerting constantly.

In your example I can think of a few cases why the observed behavior
might be happening.

One, you may have some offloading enabled on your NIC.  Best practice is
to disable it.  Check the documentation here for instructions:

> https://redmine.openinfosecfoundation.org/projects/suricata/wiki/File_Extraction

Two, I know that the unified2 logging is a "best effort" and may not
always log all packets.

I was going to mention this earlier, but if I was interested in matching
on all packets I would just use bpf filters and full-packet capture.


On 4/11/2016 2:44 PM, Shane Boissevain wrote:
> Coop,
> Thank's for the speedy reply. I've confirmed that by playing with the flags
> option i can get suricata to trip on the desired 18 packets.
> However, I suppose my question isn't so much as "how do i get this to trip
> on these packets" and more of why doesn't that signature trip on all of
> these packets?
> For example, if i add a reputation alert (based off of those found at
> Emerging Threat's drop.rules file:
> alert ip any -> any any (msg:"TEST Rule 2";
>> classtype:misc-attack; sid:9000002; rev:1;)
> I would expect there to be 20 alerts tripped, as I send 20 packets that
> have the source ip of (as verified below):
> # tcpdump -nr test.pcap src net | wc
>>      20 lines
> However, I only see 5 total alerts...verified by:
> # u2spewfoo unified2.alert.1460410545  | grep '(Event)' | wc
>>       5 lines
> ~ Shane

Cooper Nelson
Network Security Analyst
UCSD ITS Security Team
cnelson at ucsd.edu x41042

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