IPS slow under load (or packets being dropped)

[Dave Osbourne <dave () osbourne uk eu org>]

Hi,

This seems to be a repeating issue on the list, but I can't find a 
solution suggested that actually works.

I have snort configured as IPS (inline)

   config daq: afpacket
   config daq_mode: inline

"bridging" eth1 and eth2.

All is good until a large flow occurs.  Then I see messages like

 * IP truncated-ip - 1328 bytes missing!
 * packet size is too long (2843 > 1518)
 * (snort_decoder) WARNING: IP dgm len > captured len

and things start to crawl - throughout stays at around 10KB/s

snort = 2.9.8.2
daq = 2.0.6

~# snort --daq-list
Available DAQ modules:
pcap(v3): readback live multi unpriv
ipfw(v3): live inline multi unpriv
dump(v3): readback live inline multi unpriv
afpacket(v5): live inline multi unpriv

Does anyone know where I start looking?  Expecting some trouble I source 
compiled and a recompile is very quick so quite happy to go down that 
route if necessary...

Dave

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