Snort mailing list archives
RE: WHy no alerts using eth0_ADDRESS?
From: "Hutchinson, Andrew" <Andrew.Hutchinson () Vanderbilt edu>
Date: Tue, 15 Jan 2002 15:08:26 -0600
I believe that the issue is this: when you use var HOME_NET $eth0_ADDRESS then your $HOME_NET is set to the _single_ ip address of eth0. For instance, if eth0 is 192.168.1.1/32, then snort will _only_ alert when the ICMP packet is coming from or headed to eth0 on the sensor itself. So, if your ping was from the sensor, I would expect alerts, whereas if the ping is simply passing through the sensor, the $HOME_NET is not matched and thus no alert generated. However, when you have var HOME_NET 192.168.1.0/24 or the like, the entire subnet is matched by $HOME_NET, and the signature is matched and an alert generated. Hope this helps, Andrew Andrew Hutchinson CNE MCSE Informatics/NCS/Network Security Vanderbilt University Medical Center 615.936.2856 - voice 615.936.0643 - fax andrew.hutchinson () mcmail vanderbilt edu -----Original Message----- From: Dr. Richard W. Tibbs [mailto:ccamp () oakcitysolutions com] Sent: Tuesday, January 15, 2002 2:38 PM To: snort-users () lists sourceforge net Subject: [Snort-users] WHy no alerts using eth0_ADDRESS? I am puzzled mildly by some remarks in the snort.conf file: .... # # or use global variable $<interfacename>_ADDRESS # which will be always initialized to IP address and # netmask of the network interface which you run # snort at. # # var HOME_NET $eth0_ADDRESS # # You can specify lists of IP addresses for HOME_NET # by separating the IPs with commas like this: # # var HOME_NET [10.1.1.0/24,192.168.1.0/24] # # MAKE SURE YOU DON'T PLACE ANY SPACES IN YOUR LIST! # # or you can specify the variable to be any IP address # like this: #var HOME_NET any By the comments above, I am led to believe that snort will always initialize the $eth0_ADDRESS variable to the home net. Snort has always worked "out of the shrink wrap" with no mods to snort.conf and finds eth0, my only active NIC; snort -v reports packet as usual. However ...... In an exploration with snort, I tried var HOME_NET $eth0_ADDRESS output alert_unixsock alert icmp $HOME_NET any -> any any (msg: "OUT" ;) alert icmp any any -> $HOME_NET any (msg: "IN" ;) and I, when I ping another machine I get no alerts, although the snort summary output counts as many packets as ping sends & receives. (i.e., the snort output is like: Breakdown by protocol: Action Stats: ... Akerts: 0 ICMP: 12 ... But when I use var HOME_NET 192.168.1.0/32 output alert_unixsock alert icmp $HOME_NET any -> any any (msg: "OUT" ;) alert icmp any any -> $HOME_NET any (msg: "IN" ;) I get the appropriate equal amounts of INs and OUTs alerted to the socket. How come no alerts in the first case? Do I actually have to set the eth0_ADDRESS variable myself? _______________________________________________ Snort-users mailing list Snort-users () lists sourceforge net Go to this URL to change user options or unsubscribe: https://lists.sourceforge.net/lists/listinfo/snort-users Snort-users list archive: http://www.geocrawler.com/redir-sf.php3?list=snort-users _______________________________________________ Snort-users mailing list Snort-users () lists sourceforge net Go to this URL to change user options or unsubscribe: https://lists.sourceforge.net/lists/listinfo/snort-users Snort-users list archive: http://www.geocrawler.com/redir-sf.php3?list=snort-users
Current thread:
- WHy no alerts using eth0_ADDRESS? Dr. Richard W. Tibbs (Jan 15)
- <Possible follow-ups>
- RE: WHy no alerts using eth0_ADDRESS? Hutchinson, Andrew (Jan 15)