[Snort-users] snot processes packets twice?

jorbru30 at ...5068... jorbru30 at ...5068...
Wed Jun 27 15:52:34 EDT 2012

Thank you Ru ss 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 5 0,000 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 . 


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

From: "Russ Combs" <rcombs at ...1935...> 
To: jorbru30 at ...5068... 
Cc: snort-users at lists.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: 



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! 


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