[Snort-users] Snort Just Does Not Want To Work on Shadow Interrface

Rhugga snort-list at ...12135...
Tue Jul 20 06:56:03 EDT 2004

I will be as terse as possible here, because I have tried configs from 
people that claim they should work but aren't. I have read the 
documentatrion probably 5 times now, (well the documentation says 
version 1.0, the link on the website says 1.1, but the version I am 
using is 1.2)

Anyway. My system is vanilla RH 9 with all updates except I build my own 
openssl library and also using mysql 4.x in /usr/local. ( I have 
compeltely re-installed since I first started just to eliminate ANY 
possible issues because some people claim snort 1.2 works as I desire on 
RH  9)

IP address:
SysKonnect Copper GB NIC directly connected to a switch in our Black 
Diamond. (Cat 6 cabling with no patch panels in between)

IP address: None
Onboard Intel NIC connected to a 4 port hub. Also on this hub is a Cisco 
3600 router and 2 Netscreen Firewalls.

The network on the hub is 65.120.XX.XX with netmask of

Here are the contents of the /etc/sysconfig/network-scripts/ifcfg-eth1

Note: I added this after I initially tried to get it working without 
adding an IP. I saw this as a solution to some people's problems in the 
mailing list archvie.

If I look at the traffic on eth1:

syslog:/usr/local/snort/bin #./snort -i eth1 -v
Running in packet dump mode
Log directory = /var/log/snort

Initializing Network Interface eth1
OpenPcap() device eth1 network lookup:
       eth1: no IPv4 address assigned

       --== Initializing Snort ==--
Initializing Output Plugins!
Decoding Ethernet on interface eth1

       --== Initialization Complete ==--

-*> Snort! <*-
Version 2.1.3 (Build 27)
By Martin Roesch (roesch at ...1935..., www.snort.org)
07/20-06:28:39.383108 -> 65.120.XX.XX
IPV6-CRYPT TTL:52 TOS:0x0 ID:43725 IpLen:20 DgmLen:104

07/20-06:28:39.383705 -> 65.120.XX.XX
IPV6-CRYPT TTL:52 TOS:0x0 ID:43726 IpLen:20 DgmLen:104

It is reading traffic on eth1. However, when I start nagios it will run, 
but it will not match anything. I get not a single alert. However, when 
I assign eth1 a valid IP address on the 65.120.XX.XX network, it 
immediately starts matching. Within seconds my alert count starts 
climbing. (Note that when I say I am assigning it a valid IP address I 
also modify HOME_NET to reflect this)

Here is how I define HOME_NET when I am trying to use snort _without_ an 
IP address:


What am I doing wrong? According to the documentation and the responses 
to my first emails, this config is correct.

What gives??


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