[Snort-users] OpenPcap()

Justin Heath justin.heath at ...11827...
Tue Jun 20 15:59:57 EDT 2006


This was posted from Steve Sturges a little while back on snort-users:

"As noted in the RELEASE.NOTES, there was a change in the
default pattern matching engine from Wu-Manber to standard
Aho-Corasick which is faster but consumes more memory.

This effectively replaced an implicit config of

config detection: search-method mwm

with

config detection: search-method ac

The Aho-Corasick implementation in snort has a few different
memory models, standard, full, banded, sparse, and sparse
banded.  The sparse and spare-banded ones consume much less
memory... To use them, add a snort.conf line, as desired,
for example.  Wu-Manber is being deprecated in the next
release.

config detection: search-method ac-sparsebands

There is also the lowmem method, which is slow, but uses
very little memory."

On 6/20/06, Gentoo-Wally <gentoowally at ...11827...> wrote:
>
> Thx. So do you think a jump from 25% usage in 2.4.5 to 90% usage in
> 2.6.0 on a machine with 1Gb ram should be expected?
>
> On 6/20/06, Joel Esler <joel.esler at ...1935...> wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > Snort 2.6 uses more memory than it's predecessors.  The OpenPcap msg you
> > saw is normal, it's just telling you that there is no IP assigned to the
> > sniffing interface (eth0).  Which, if you are using a promisc card
> > interface with no IP, is exactly what you want...
> >
> > Joel
> >
> > Gentoo-Wally wrote:
> > > I've started looking at snort 2.6.0 and have run into something
> strange.
> > >
> > > Compile info:
> > > 1. gcc 4.1.1
> > > 2. ./configure --enable-dynamicplugin --enable-dependency-tracking
> > > --with-libpcap-includes=/usr/include/
> > > --with-libpcap-libraries=/usr/lib/
> > > 3. Have tried libpcap 0.9.4 and the current version of phil woods
> libpcap
> > > 4. Gentoo Linux box
> > > 5. 'ifconfig eth0 up promisc' to bring the interface up
> > >
> > > No errors during ./configure && make && make install
> > >
> > > when I start snort it hangs for 15-30 seconds at...
> > >
> > > Initializing Network Interface eth0
> > > OpenPcap() device eth0 network lookup:
> > >         eth0: no IPv4 address assigned
> > > Decoding Ethernet on interface eth0
> > >
> > >
> > > I'm starting it like this..
> > >
> > > /usr/local/bin/snort -i eth0 -u snort -l /var/log/snort -c
> > > /usr/local/etc/snort/snort.conf
> > >
> > > also tried...
> > >
> > > /usr/local/bin/snort -i eth0 -l /var/log/snort -c
> > > /usr/local/etc/snort/snort.conf
> > >
> > >
> > > At this point memory consumption sky rockets to 95% usage even with
> > > all preprocessors except flow turned off. After about 30 seconds it
> > > finishes initializing and appears to work correctly but at 95% memory
> > > consumption and swap usage begins kicking in.
> > >
> > > I googled the OpenPcap message but found nothing that seems relevant
> > > to my situation.
> > >
> > > I also have a snort 2.4.5 install on the same box. When it starts I do
> > > not see the OpenPcap message and it works flawlessly at around 18-24%
> > > mem usage with all preprocessors on.
> > >
> > > I also tried compiling 2.6.0 without the new dynamic preprocessors or
> > > the dep tracking and I still get the openpcap message and crazy mem
> > > usage.
> > >
> > > Any ideas?
> > >
> > > Wally
> > >
> > >
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> > >
> >
> > - --
> > +---------------------------------------------------------------------+
> > Joel Esler           Senior Security Consultant         1-706-627-2101
> > Sourcefire    Security for the /Real/ World -- http://www.sourcefire.com
> > Snort - Open Source Network IPS/IDS -- http://www.snort.org
> > GPG Key http://demo.sourcefire.com/jesler.pgp.key
> > +---------------------------------------------------------------------+
> > -----BEGIN PGP SIGNATURE-----
> > Version: GnuPG v1.4.3 (Darwin)
> > Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org
> >
> > iD8DBQFEmBrGKbCSyXHckt4RAq9HAJ45D9emK3cHcWf7WoR+Ex1DmykHlQCgovM3
> > cxap2QpG64S7+k8Tr2UOvLQ=
> > =xdKQ
> > -----END PGP SIGNATURE-----
> >
>
>
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