[Snort-users] Problem running Snort Inline

James Lay jlay at ...13475...
Thu Feb 5 08:42:25 EST 2015


On Thu, 2015-02-05 at 06:40 +0000, Anshuman Anil Deshmukh wrote:
> Hi,
> 
>  
> 
> We have issues running Snort inline. This is the exact problem which
> is mentioned here -
> http://www.linuxforums.org/forum/debian-linux/200751-snort-inline.html
> (see log below).
> 
>  
> 
> We have setup the Snort inline (version 2.9.7.0) which is compiled
> using switch --enable-sourcefire. 
> 
>  
> 
> It says “Enabling inline operation” and then switches to IDS mode. 
> 
>  
> 
> Our command line for running Snort:
> 
> /usr/local/snort/bin/snort
> -c /usr/local/snort/etc/snort_conf_rules.conf -i eth0:eth1 -Q
> --pid-path=/var/run which creates the bridge automatically. Both the
> interfaces doesn’t have IP addresses assigned.
> 
>  
> 
> We have already enabled following options for snort inline:
> 
> config policy_mode:inline
> 
> config daq: afpacket
> 
> config daq_mode: inline
> 
> config daq_var: buffer_size_mb=1024
> 
>  
> 
> preprocessor normalize_ip4
> 
> preprocessor normalize_tcp: ips ecn stream
> 
> preprocessor normalize_icmp4
> 
> preprocessor normalize_ip6
> 
> preprocessor normalize_icmp6
> 
>  
> 
> Under verdicts it shows 0% packets blocked. We have enabled couple of
> drop rules for BRUTE FORCE attack one of which is getting detected.
> Here is the snort output.
> 
> 02/02-12:12:23.042082  [Drop] [**] [1:2019876:2] ET SCAN SSH
> BruteForce Tool with fake PUTTY version [**] [Classification:
> Detection of a Network Scan] [Priority: 3] {TCP} 000.000.000.00:38772
> -> 00.00.00.:22 (IP addresses information removed)
> 
>  
> 
> But under verdicts it shows nothing blocked. Why??
> 
>  
> 
> Verdicts:
> 
>       Allow:      4335107 ( 59.187%)
> 
>       Block:            0 (  0.000%)
> 
>  
> 
> Output says:
> 
> Enabling inline operation
> 
> Running in IDS mode
> 
>  
> 
>         --== Initializing Snort ==--
> 
> Initializing Output Plugins!
> 
> Initializing Preprocessors!
> 
> Initializing Plug-ins!
> 
>  
> 
> ===============================================
> 
> Information about our setup-
> 
>  
> 
>    ,,_     -*> Snort! <*-
> 
>   o"  )~   Version 2.9.7.0 GRE (Build 149) 
> 
>    ''''    By Martin Roesch & The Snort Team:
> http://www.snort.org/contact#team
> 
>            Copyright (C) 2014 Cisco and/or its affiliates. All rights
> reserved.
> 
>            Copyright (C) 1998-2013 Sourcefire, Inc., et al.
> 
>            Using libpcap version 1.4.0
> 
>            Using PCRE version: 7.8 2008-09-05
> 
>            Using ZLIB version: 1.2.3
> 
>  
> 
> ============================================================================
> 
>  
> 
> /usr/local/snort/bin/snort --daq-list
> 
> Available DAQ modules:
> 
> pcap(v3): readback live multi unpriv
> 
> ipfw(v3): live inline multi unpriv
> 
> dump(v2): readback live inline multi unpriv
> 
> afpacket(v5): live inline multi unpriv
> 
>  
> 
> ===========================================================================
> 
>  
> 
> Please let me know in case any other information is required.
> 
>  
> 
>  
> 
> Regards,
> 
> Anshuman
> 
>  


>From snort-2.9.7.0/doc/README.daq:

Configuring Snort
=================

Assuming that you did not disable static modules or change the default
DAQ
type, you can run Snort just as you always did for file readback or
sniffing an
interface.  However, you can select and configure the DAQ when Snort is
invoked
as follows:

    ./snort \
        [--daq <type>] \
        [--daq-mode <mode>] \
        [--daq-dir <dir>] \
        [--daq-var <var>]

    config daq: <type>
    config daq_dir: <dir>
    config daq_var: <var>
    config daq_mode: <mode>

    <type> ::= pcap | afpacket | dump | nfq | ipq | ipfw
    <mode> ::= read-file | passive | inline
    <var> ::= arbitrary <name>=<value> passed to DAQ
    <dir> ::= path where to look for DAQ module so's

And from the daq README:

AFPACKET Module
===============

afpacket functions similar to the pcap DAQ but with better performance:

    ./snort --daq afpacket -i <device>
            [--daq-var buffer_size_mb=<#MB>]
            [--daq-var debug]

If you want to run afpacket in inline mode, you must craft the device
string as
one or more interface pairs, where each member of a pair is separated by
a
single colon and each pair is separated by a double colon like this:

    eth0:eth1

or this:
    eth0:eth1::eth2:eth3

I think you want:  snort --daq afpacket --daq-mode inline -i eth0:eth1

I believe -Q and --daq-mode inline work about the same.  Hope that
helps.

James
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