[Snort-users] new user - snort is not droping pacekts

Alex Butcher, ISC/ISYS Alex.Butcher at ...11254...
Tue Feb 15 05:40:30 EST 2005

--On 15 February 2005 10:47 +0100 lokesh.khanna at ...13040... wrote:

> Thanks again for reply.
> But it is confusing me more. As per my knowledge I can not set a rule
> using IPCHAIN which will drop a packets based on content in the packet.
> What I am able to understand is if I use IDS in INLINE mode, IDS will
> act as a router and based on alerts, IDS will insert rules in IPTABLE.

See <http://www.snort.org/docs/snort_manual/node7.html>

Essentially, when running in inline mode, Snort can either cause the 
*packet* matching a rule to be dropped (with or without logging), or it can 
reject the packet (using TCP RST or ICMP dest unreachable packets) so as to 
terminate the session.

Snort running in inline mode won't blacklist all traffic from 
alert-generating hosts, unless you use flexresp or snortsam to tie it in 
with a firewall (be that iptables/netfilter, Cisco, or FW-1)

> I can have a genuine traffic from an IP address and virus traffic from
> same IP address. So content of that packet will define if packet should
> drop or it should not. How IPCHAIN will handle this?

To be honest, this perhaps isn't the best place to ask about snort inline - 
I haven't used it, so everything I've told you has come from reading the 
snort manual, <http://snort-inline.sourceforge.net/index.html> and 

> Cordially,
> LK


> -----Original Message-----
> From: Alex Butcher, ISC/ISYS [mailto:Alex.Butcher at ...11254...]
> Sent: 15 February 2005 10:34
> To: Lokesh Khanna; snort-users at lists.sourceforge.net
> Subject: RE: [Snort-users] new user - snort is not droping pacekts
> --On 15 February 2005 10:23 +0100 lokesh.khanna at ...13040... wrote:
>> I remember in real secure or manhunt, I used to configure a port in
>> mirroring mode on switch and I put IDS on that port. All our traffic
> was
>> going through that mirrored port. Based on rules defined in IDS, it
> was
>> dropping / logging packets.
> Logging, yes, but those products would only have been dropping (i.e.
> blocking, rejecting) packets if they were interacting with a firewall or
> router in some way (or they were running in some kind of IPS mode, which
> you seem to indicate was not the case).
>> If I understand correctly, do I need to pass all traffic through IDS
>> box.
> If you're using inline mode, yes, the snort machine will be acting as a
> router (actually an Intrusion _Prevention_ System or IPS). See
> <http://snort-inline.sourceforge.net/> and README.INLINE for more info
> on
> inline mode. Note that 2.3.0 integrates the inline stuff IIRC.
>> IDS will act as a router also. And based on alerts, IDS will make
>> modification in IPCHAIN and will drop or allow packets.
> See the above site for the details.
>> Or is there any other way out? How can I find out documents on this?
> <http://www.snortsam.net/> and README.FLEXRESP and README.FLEXRESP2 in
> the
> snort docs.
>> Cordially,
>> LK
> Best Regards,
> Alex.

Alex Butcher: Security & Integrity, Personal Computer Systems Group
Information Systems and Computing             GPG Key ID: F9B27DC9
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