Snort mailing list archives
Re: Snort dont understand pf (openbsd) format
From: Matt Kettler <mkettler () evi-inc com>
Date: Mon, 29 Nov 2004 22:16:52 -0500
At 08:52 PM 11/29/2004, Sean Brown wrote:
> It's unclear if OpenBSD generates real tcpdump files that any ordinary > tcpdump can read, or if they patched tcpdump to support them.It doesn't, it is a modified format that the tcpdump in OpenBSD was patched toread. However, in the FAQ: 4.4 Does snort see packets filtered by IPTables/IPChains/IPF/PF? ... Under OpenBSD you can snort just the PF rejects by using the /dev/pflogN interface. Since pflogd simply writes the traffic from pflog, snort should be able to understand the log file, but I have tried to have it read the file and attached it to /dev/pflog0 and it does not understand the traffic. Perhaps the output format changed in one of the recent OpenBSD releases and Snort was never updated. If so, the FAQ needs to be fixed.
Since so many people are responding off list, I'll take a chance to respond on-list.
Summary - snort does support PF format log files via -r and pflog devices via -i.
However, it only supports said format on a system which has a libpcap/tcpdump version that is PF aware. If bpf.h doesn't define the PF datalink type, snort will not handle pf files or devices and will generate errors if fed them.
The PF log format is an extension of the list of data link formats available to pcap, and has been merged to the main tree. The PF "data link" adds a header that defines things like what happened to the packet and what ruleset is responsible.
Newer releases of libpcap and tcpdump include support for this format, older ones don't.
The Breno is running snort on a Linux box, and is trying to parse files gathered from an OpenBSD box. It appears that some Linux distros include the newer releases, others don't. It appears that Breno's Linux box has a non-pf-aware version of libpcap/tcpdump. Since snort can't find the defines it needs when built on such a system, PF support disappears. Running pf files in generates an unknown data link type error as a result.
As an aside, the FAQ entry is semi-irrelevant to this thread. That faq is about using snort to listen pflog DEVICES using snort -i /dev/pflog0, not parse pflog FILES via snort -r /var/log/pflog. Two totally different things.
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Current thread:
- Snort dont understand pf (openbsd) format Breno Leitão (Nov 29)
- Re: Snort dont understand pf (openbsd) format Matt Kettler (Nov 29)
- Re: Snort dont understand pf (openbsd) format Matt Kettler (Nov 29)
- Re: Snort dont understand pf (openbsd) format Sean Brown (Nov 29)
- Re: Snort dont understand pf (openbsd) format Matt Kettler (Nov 29)
- Re: Snort dont understand pf (openbsd) format Sean Brown (Nov 29)
- Re: Snort dont understand pf (openbsd) format Matt Kettler (Nov 30)
- Re: Snort dont understand pf (openbsd) format Matt Kettler (Nov 30)
- Re: Snort dont understand pf (openbsd) format Christian Robottom Reis (Nov 30)
- Re: Snort dont understand pf (openbsd) format Sean Brown (Nov 30)
- Re: Snort dont understand pf (openbsd) format Christian Robottom Reis (Dec 01)
- Re: Snort dont understand pf (openbsd) format Jeremy Hewlett (Dec 01)
- Re: Snort dont understand pf (openbsd) format Breno Leitão (Dec 02)
- snort patch to understand pflog (ond and new) Breno Leitão (Dec 03)
- Re: Snort dont understand pf (openbsd) format Matt Kettler (Nov 29)
- Re: Snort dont understand pf (openbsd) format Matt Kettler (Nov 29)
- Re: Snort dont understand pf (openbsd) format M. Shirk (Dec 01)