Re: Snort running inline but not functioning as IPS

[Robin Kipp <mlists () robin-kipp net>]

Hi YM,
thanks for all your hints and ideas!
Before I start commenting on them in greater detail, let me start by saying that I completely wiped Snort, Barnyard2 
and Pulledpork (including all files and databases) from the system in order to start from scratch.
After reinstalling Snort, I started by creating an ICMP detect rule, which I first set to alert („alert ICMP…“). After 
running Snort in IDS mode, the ICMP packets were successfully detected and the alerts were logged.
Then, I went back and edited the rule, changing „alert“ to „drop“. Then, I once again started Snort, this time in 
inline mode using DAQ-NFQ. At that point, when trying to execute pings, Snort would not only alert on them but also 
drop the packets like it was supposed to.
Next I proceeded by reinstalling Pulledpork, setting IPS policy to „balanced“ before downloading / processing any 
rules. The downloading and processing then proceeded without errors, afterwards I fired up Snort once again to see what 
would happen. Sadly, I then discovered that this took me right back to where I started, over 7000 rules loaded but no 
alerts or other visible reactions to rules being triggered… I can see in the stats that Snort is capturing traffic 
alright, but it’s still dead quiet about alerts!
However, I made a very interesting discovery: once I edited my pulledpork.conf and commented out ips_policy, then 
reprocessed rules with the -P flag, Snort would once again generate alerts properly. After changing ips_policy to 
either „balanced“ or „security“, Snort would go back to being silent.
> Am 24.01.2016 um 22:26 schrieb Y M <snort () outlook com>:
>
> If you run tcpdump on the same box where snort is installed, do you see the traffic on the the same NIC snort is 
> listening to?

Yes, I can confirm that this traffic is in deed passing through that NIC, so my setup should be alright I suppose...
> Also, since you are using NFQ, could iptables got misconfigured somehow? Just thinking out loud.

Well, of course there’s always a chance for that! :-) However, since I tested this both in IDS mode (simply specifying 
the NIC using the -i flag) with the same result and also since it worked just fine before with only one ICMP rule, I 
don’t think that iptables is the problem.
> Try also to disable NIC offloading stuff, or run snort with the -k none for testing purposes and see if that helps.

Yep, I have both GRO and LRO disabled, that was something I did even before running Snort for the very first time. I 
have also verified that it’s still disabled using ethtool, everything looks just fine to me.
So, after all this I can’t shake off the feeling that Pulledpork may be doing something odd with those rules, because 
as far as I can tell Snort works just fine! Is there perhaps any other rule management software that I could use? All 
the Snort tutorials that I’ve looked at talk about Pulledpork, so I’m not really expecting a positive answer here… I’m 
just desperately seeking a solution, because this looks like I’m really close to getting it all up and running except 
for this annoying issue.
Just a few minutes ago, I tried running snort with the -v flag which showed me pretty much all the connections on my 
network as far as I can tell, so the packet capturing really works. Now, if only I could get it to actually generate 
those alerts…
Thanks for any more help!!!
Best regards,
Robin
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