[Snort-users] snot processes packets twice?

jorbru30 at ...5068... jorbru30 at ...5068...
Wed Jun 27 23:11:48 EDT 2012

Hi Rmkml , Russ, 


I think I resolved the issue after a number of trials. The issue was with my deployment. I was routing the traffic instead of switching. 


Here is a more elaborate description of my deployment. 

A <-> eth0(<.->eth1(<->B 

A generates HTTP traffic and routes it to eth0 (A gateway is eth0) 

B responds to HTTP requests through its gateway eth1. 

Snort runs on  Ubuntu box and has eth0 and eth1 as its incoming and outgoing interfaces. 


When I changed my deployment to switching instead of routing traffic, it works perfectly. Th packets that snort processes are exactly what is transmitted through the snort box.  


In my old setup, it looks received and transmitted packets are seen as different by snort as it packets are modified when routed. 


Thank you!!!  


Jorda . 

----- Original Message -----

From: " rmkml " < rmkml @yahoo.fr> 
To: jorbru30 at ...5068... 
Cc: "Russ Combs" < rcombs @ sourcefire .com>, snort-users at ...8192... sourceforge .net, rmkml @yahoo.fr 
Sent: Wednesday, June 27, 2012 3:59:39 PM 
Subject: Re: [Snort-users] snot processes packets twice? 

Can you try with last snort stable v2.9.2.3 and daq v0.6.2 ? 
or latest snort release candidate (v2.9.3_ rc ) and daq v1.1.1 ? 
Can you run daq dump ? 

On Wed, 27 Jun 2012, jorbru30 at ...5068... wrote: 

> Thank you Russ for the tip. 
> I checked for any bridge but there is none. 
> mysnort @home:~/ pcaps $ brctl show 
> bridge name bridge id   STP enabled interfaces 
> I captured pcaps at eth0 and eth1 and each show about 25,000 packets. 
> I also added a print statement prior to " ProcessPacket " in snort.c to verify snort is indeed inspecting duplicate packets. My findings is yes, it does inspect about 50,000 packets. 
> I am still trying to figure out why snort checks packets from both interface and how to fix the issue. 
> I appreciate any help. 
> Jorda .  
> ____________________________________________________________________________________________________________________________________________________________________________________________________________________________ 
> From: "Russ Combs" < rcombs @ sourcefire .com> 
> To: jorbru30 at ...5068... 
> Cc: snort-users at ...8192... sourceforge .net 
> Sent: Wednesday, June 27, 2012 10:56:47 AM 
> Subject: Re: [Snort-users] snot processes packets twice? 
> Not sure why you are seeing double; any chance you bridged eth0 and eth1? 
> On Wed, Jun 27, 2012 at 1:18 AM, <jorbru30 at ...5068...> wrote: 
>       Hi, 
>       I am running snort version 2.9.1 as IPS using the following command. 
>       / usr /local/snort/bin/snort -- daq afpacket -i eth0:eth1 -Q -- daq -dir=/ usr /local/lib/ daq -l /var/log/snort -c / usr /local/snort/etc/snort. conf 
>       I am sending packets from a traffic generator tool which acts as a sender and receiver. 
>             Traffic generator( TGS )<-> eth0 <->eth1 <-> Traffic generator( TGR ) 
>       About 25,000 packets are seen at eth0 (packets sent from TGS and responses(mostly ack packets) from TGR ).  The same set of packets are seen at eth1. 
>       After I stopped snort with ctr-c, snort displays ..."Snort processed 50531 packets". 
>       I was expecting snort to process incoming packets (packets from eth0 to eth1) and outgoing packets (packets from eth1 to eth0) which is about 25,000 but it processes double # of packets. 
>       Please help me understand why snort process packets twice. 
>       Thank you! 
>       Jorda .
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