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snort suddenly not capturing packets
From: Ben Jacobs-Swearingen <bjsdaiyu () gmail com>
Date: Wed, 8 Jan 2014 19:39:02 -0500
I recently restarted snort on an ArchLinux ARM (Raspberry Pi) sensor with
new rules (and a slightly modified snort.conf) ; the post-reboot snort will
launch without explicit errors but appears not to be listening to any
interfaces on the sensor and I am unable to figure out why. Snort had been
working correctly for months prior to this change.
The sensor has two interfaces, eth0 and eth1; mirrored traffic (for snort
to process) is being sent to eth0 (which is up and running though it does
not have a configured IP address), while eth1 has a configured address on
an admin segment. prior to changing the rules and rebooting snort, snort
was listening to and correctly processing traffic on eth0.
- "tcpdump -i eth0" works just fine, it sees all mirrored traffic
- "snort -dev -l . -i eth0" makes it to the "listening" stage but appears
to not pick up any of the traffic i generate across the interface; again,
tcpdump sees this traffic just fine. "snort -dev ..." also does not work
when I set it to listen on eth1 (tcpdump works there as well).
- "snort -r <bad.pcap> -c .../snort.conf" with <bad.pcap> containing
traffic I want flagged DOES work correctly: the traffic is processed
according to the rules, alerts are correct and sent to the correct
I suspect my changes to snort.conf might have introduced a problem that I
simply am not seeing so have attached the conf file for examination (but am
confused in that case why "snort -r" is working since it's using the same
Alternately, I have attached an strace in case something with the interface
setup somehow got screwed up (as suggest by the fact that snort replay is
working). I see in strace there are some errors with setsockopt(...) which
might be more relevant to the capturing issue; any idea what might be
causing those, assuming that those aren't par for the course?
The only similar posts I could find on this topic discuss various issues
with DAQ; I don't see how those might apply in my case since the
installation was working for months prior to today.
Thanks for any help.
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- snort suddenly not capturing packets Ben Jacobs-Swearingen (Jan 09)