Snort mailing list archives
behavior file vs. device capturing
From: Felix Erlacher <felix.erlacher () uibk ac at>
Date: Mon, 27 Nov 2017 17:58:07 +0100
Dear all, while I was trying to further investigate an alert, I stumbled upon a strange behavior that I was able to reproduce the following way: If I send an HTTP request to a local HTTP server and have snort listen on the NIC, everything behaves as I would expect it to do. Now if I make snort read the pcapng file that I captured (with wireshark) during this attempt the TCP stream preprocessor behaves differently, triggering 3 timeouts and discarding one packet (which finally leads to snort not triggering the alert contained in the HTTP request). What makes snort behave differently when configured to read from file compared to the configuration when reading from a NIC interface? Below you find the stream statistics for both runs. I use snort 2.9.11 with daq 2.0.6 compiled from source on Debian 8 (kernel 3.16). The snort.conf is the original one from the tarball. ----------------------------- sudo snort -c /etc/snort.conf -k none -i wlan0: ----------------------------- Stream statistics: Total sessions: 1 TCP sessions: 1 TCP StreamTrackers Created: 1 TCP StreamTrackers Deleted: 1 TCP Timeouts: 0 TCP Segments Queued: 2 TCP Segments Released: 2 TCP Rebuilt Packets: 2 TCP Segments Used: 2 TCP Discards: 0 TCP Port Filter Tracked: 10 ----------------------------- sudo snort -c /etc/snort.conf -k none -r ~/justCaptured.pcapng: ----------------------------- Stream statistics: Total sessions: 1 TCP sessions: 1 TCP StreamTrackers Created: 2 TCP StreamTrackers Deleted: 2 TCP Timeouts: 3 TCP Segments Queued: 0 TCP Segments Released: 0 TCP Rebuilt Packets: 0 TCP Segments Used: 0 TCP Discards: 1 TCP Port Filter Tracked: 10 Thanks and regards Felix _______________________________________________ Snort-users mailing list Snort-users () lists snort org Go to this URL to change user options or unsubscribe: https://lists.snort.org/mailman/listinfo/snort-users Please visit http://blog.snort.org to stay current on all the latest Snort news! Please follow these rules: https://snort.org/faq/what-is-the-mailing-list-etiquette
Current thread:
- behavior file vs. device capturing Felix Erlacher (Nov 27)