[Snort-users] Snort inline SLOW

Will Metcalf william.metcalf at ...11827...
Wed Apr 7 19:48:15 EDT 2010

I think it would actually make sense that it would act the same, as
ip_queue is implemented as a compatibility layer on top of
netfilter_queue on kernels that support both if I remember correctly.
With that said, is it possible that you have not modified your
ip_queue_maxlen setting and you are actually dropping packets?  You
should be able to see a dropped packet count with

cat /proc/net/ip_queue

If you are seeing dropped packets, try the following.

echo 65535 > /proc/sys/net/ipv4/ip_forward

Also see the following post Victor Julien did on improving
snort_inline performance with NFQ.


An additional thing to check is to make sure you have not accidentally
converted any alert rules intended for protocol decode to drop, grep
for flowbits:noalert, and review, as snort will silently be dropping
traffic without telling you about it.



On Wed, Apr 7, 2010 at 2:47 PM, Tomás Heredia
<tomas.heredia at ...12297...> wrote:
> Hi!
> El 07/04/2010 03:25 p.m., rmkml escribió:
>> ok thx Tomas,
>> if you start snort without/minimal rules? (comments all line contains
>> include ...rules)
> same commenting out ALL rules, preprocessors and dynamic detection
> plugins (including engine)
>> maybe send snort log to the list?
> I´ll try to send it later. Making some tests right now with the same
> machine.
>> what is network bandwith/packetspersecondes?/packetsizes through
>> snort_inline?
> Bandwith REALLY low. Just trying to browse files on a samba. I´d have to
> look for packet sizes. Tried with 1492 byte pings, and no loss at all. I
> gess some other "heavy traffic" protocols (like smb) would also fail.
> I´m gessing it could be something related to iptables. I happens both
> with ip_queue and nfnetlink_queue (cheeting here: also tried a custom
> version using some snort_inline patches, but this is not the problem as
> it also hapens with mainline snort)
> Tanks!
>> Regards
>> Rmkml
>> On Wed, 7 Apr 2010, Tomás Heredia wrote:
>>> Hi!
>>> No (more :-)) cable errors
>>> Disabling snort, and letting all the traffic thru the bridge works OK!
>>> Thanks!
>>> El 07/04/2010 03:07 p.m., rmkml escribió:
>>>> Hi Tomas,
>>>> maybe bad cable?
>>>> do you have network interface errors/collisions?
>>>> if you disable snort inline, do you have same pb?
>>>> Regards
>>>> Rmkml
>>>> On Wed, 7 Apr 2010, Tomás Heredia wrote:
>>>>> Hi all!
>>>>> I´m having a problem with inline snort, and I´d like to know if anyone
>>>>> has any clue.
>>>>> Y was using snort in inline mode int an HP DL120, on Debian
>>>>> Lenny with NO problems.
>>>>> Next, I was trying to use it on an HP DL160  on Ubuntu Karmik, with a
>>>>> TERRIBLE performance. Pings go thru OK, but I can barely browse
>>>>> windows
>>>>> folders, if at all.
>>>>> Same changing to Snort Same with empty configuration
>>>>> (always in
>>>>> inline mode).
>>>>> Any clues?
>>>>> TIA!
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