[Snort-users] Ethernet Tap

Turnquist,Wayne WayneTurnquist at ...12076...
Fri Aug 13 12:45:09 EDT 2004

im new at snort and thought i had it setup right.

i have snort with 3 interface cards and have 2 cisco fasthub 400 series where i have 1 tied to a span port(100 full) off a cat400 for mirroring a router port on one vlan. i have 1 snort interface plugged into this hub at 100 full.

should i be setting the span port for the hub at 100 half instead of 100 full?
what about the snort interface, 100 half or full?

the other hub is setup like the first but is span a different router on a different vlan


-----Original Message-----
From: snort-users-admin at lists.sourceforge.net
[mailto:snort-users-admin at lists.sourceforge.net]On Behalf Of Matt
Sent: Friday, August 13, 2004 2:15 PM
To: STEVE MAKOUSKY; snort-users at lists.sourceforge.net
Subject: Re: [Snort-users] Ethernet Tap

At 02:31 PM 8/13/2004, STEVE MAKOUSKY wrote:
>Has anyone had any luck using the tap that is described in the Doc area?

I've not used that particular tap, but looking at it the tap should work 

>Is there any instructions out there for building a full duplex tap?

A full-duplex single-port tap, by it's very nature, is going to have to 
contain a considerable amount of electronics, and cannot be a passive 
device. You can't funnel two 100mbit streams into a single 100mbit port 
without some packet buffering, re-ordering, etc, so it's going to have to 
have onboard memory, etc.

I'd suggest buying a managed switch with a span port, it's much easier and 
cheaper than trying this route, or try the interface bonding trick 
mentioned below.

>If not is it easy enough to start snort on two nics and log to the same 
>database and
>handle packet reconstruction that way????

Actually, rather than try to sniff two interfaces, most people create a 
bonded interface that combines the two, and run snort on that. Recent 
versions of Linux and *BSD support interface bonding in the kernel.


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