[Snort-users] Can Snort monitor multiple VLANs on a VM?

elof at ...6680... elof at ...6680...
Fri Apr 9 10:46:55 EDT 2010

I don't really follow your description, but...

If your sniffer NIC receive VLAN-tagged (802.1q) packets, verify if one 
unique TCP session use two separate VLANs.

Like: tcpdump -evnli eht0 -s0 -c30    <-- do NOT add any bpf filter

If you see a SYN from A to B tagged with VLAN 1 and the SYN+ACK response 
from B to A tagged with VLAN 2, then snort won't create alerts since the 
state can't be determined (and usually all rules use flow: established).

This is a common problem with SPAN in HP switches.

However, if both SYN and SYN+ACK are tagged with the same VLAN, snort 
should be able to handle the traffic. Make sure you don't use any bpf 
filter though! Like if you run snort with the filter "ip and not esp", 
then you won't match a single VLAN packet (then you need 'vlan and ip and 
not esp').


On Fri, 9 Apr 2010, Jun Wan wrote:
> In my physical Accer machine, all I did was to mirror the network traffic form the uplink fiber port (source) to the port (destination) the Accer box is connected to (these two ports are on the same switch).
> Is this the question you asked me? ---- port mirroring configuration on switch?
> I don't know what to configure on switches for my VM's case, this is because of all 3 NICs on my VM are virtual NICs, which are not really relevant to any physical ports on the switches.
> Please see more details of ESX enviroment and how ESX machines are connected to our cores.
> If we can't configure ports to monitor those vlans on a VM, then Snort wouldn't be able to monitor in a VM environment. Is that right? Any information and help would be much appreciated.
> Thanks again.
> Regards
> John
> ----------------------------------------
>> Subject: RE: [Snort-users] Can Snort monitor multiple VLANs on a VM?
>> Date: Thu, 8 Apr 2010 16:15:36 -0500
>> From: Kirby.Boteler at ...14814...
>> To: junwei_wan at ...125...
>> Have you configured your switch port to monitor those vlans?
>> Kirby Boteler | Director of Information Technology
>> Waggoner Engineering, Inc. | 143-A LeFleurs Square | Jackson, MS 39211
>> office: (601) 355-9526 | ÿÿ fax: (601) 352-3945 | kirby.boteler at ...391...4814...
>> -----Original Message-----
>> From: Jun Wan [mailto:junwei_wan at ...125...]
>> Sent: Thursday, April 08, 2010 1:13 AM
>> To: snort-users at lists.sourceforge.net
>> Subject: [Snort-users] Can Snort monitor multiple VLANs on a VM?
>> Hi,
>> I am new to Snort, I followed the instructions on this url: https://wwwx.cs.unc.edu/~hays/archives/work/index.php
>> All went well, Snort is running well and I am having many Snort alerts in the BASE and terminal.
>> Snort and Barnyard2 in Ubuntu 9.10 is running on My Accer box with dual core Intel CPU @1.86 GHZ, 80G HD.
>> There is only one 10/100 NIC on my Accer box, so monitoring and management
>> are on the same interface. Snort is monitoring only one VLAN (VLAN1) at moment.
>> Now I would like to use Snort to monitor multiple VLANs, e.g. VLAN 1, VLAN 20 etc, so I converted my Accer-Ubuntu-Snort box into a VM in our ESX4.0 environment, I created two additional NICs on the VM, now there are three NICs;:NIC1 is for management on VLAN1, NIC2 is for monitoring on VLAN1, and NIC3 is for monitoring on VLAN20.
>> After lots of ÿÿGoogleÿÿ, I have found the following post from Barry (in 2005) is really relevant to my case:
>> http://seclists.org/snort/2005/q2/60
>> I have got the idea, but itÿÿs still hard for me to follow the actual ÿÿHOW TOÿÿ steps. I donÿÿt expect anyone to do ÿÿbaby-sitterÿÿ on Snort, despite Barry did a very good ÿÿcase studyÿÿ, but I would like to have some extra info regarding the files, locations, what, how etc (just like the first url link above from Bil) for the Snort dummy like me.
>> I would like to have the followings:
>> 1.) How to setup the management interface separately from the monitoring interface?
>> 2.) How to setup two instances of Snort and Barnyard to monitor two VLANs on one VM?
>> * Network ports (for ESX 4.0 machines) on switch are configured in the followings:
>> hybrid link type
>> with VLAN 1, VLAN 20 tagged, and
>> the hybrid PVID is VLAN20.
>> Any information and help would be much appreciated.
>> Many thanks in advance.
>> Regards
>> John
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