Re: Inline snort negative impact on network

[Y M <snort () outlook com>]

Date: Thu, 13 Nov 2014 12:09:45 -0800
From: charles.heselton () gmail com
To: snort-users () lists sourceforge net
Subject: Re: [Snort-users] Inline snort negative impact on network

YM,
I'm not sure what "lro, gro, and the rest of the gang" means, or what is involved in dis-/enabling them.

I have tweaked the RX/TX buffers.  Here are (some of) the tuning changes I've made in /etc/sysctl.conf:# Performance 
settingsnet.core.netdev_max_backlog = 10000net.core.r mem_default = 16777216net.core.rmem_max = 
33554432net.ipv4.tcp_mem = 194688 259584 389376net.ipv4.tcp_rmem = 1048576 4194304 33554432net.ipv4.tcp_no_metrics_save 
= 1net.ipv4.tcp_sack = 0# IF also in Inline mode:net.core.wmem_default = 16777216net.core.wmem_max = 
33554432net.ipv4.tcp_wmem = 1048576 4194304 16777216# Memory handling ? not that 
importantvm.overcommit_memory=2vm.overcommit_ratio = 50
These tunings are based on various article I've found while googling.
I will tak a look at the http_inspect configuration.
Thanks again, for the advice.
## Sorry I wasn't clear. These are the NIC offloading options which are not desired when sniffing packets as they 
"manipulate" how packets are presented to kernel/Snort.  For example, for LRO and GRO: 
http://manual.snort.org/node7.html. There are other offloading features that may need to be disable as well, such as 
GSO, TSO. Run ethtool -k <interface> to see what is enabled/disabled and then use ethtool -K to disable them as 
mentioned in the link.
What I meant by the RX/TX buffers are the NIC ones, not only the kernel's. Use the ethtool again (with -g and -G) to 
determine/modify the values of the buffers: http://linux.die.net/man/8/ethtool. What daq mode are running?
YM

On Thu, Nov 13, 2014 at 10:07 AM, Y M <snort () outlook com> wrote:



Date: Thu, 13 Nov 2014 09:46:24 -0800
Subject: Re: [Snort-users] Inline snort negative impact on network
From: charles.heselton () gmail com
To: snort () outlook com
CC: snort-users () lists sourceforge net



On Wed, Nov 12, 2014 at 10:59 PM, Y M <snort () outlook com> wrote:



I would say tuning; NIC (gro, lro, etc), kernel (networking stack), and Snort itself (number of rules/processors, etc). 
Since you are already on Snort 2.9.7.0, why not using daq 2.0.4? And there is the "unknown/unexpected" hardware 
behavior. If all the tuning does not improve things, see if you can test with different NICs if possible.
YM


I've done some sysctl tuning, but it hasn't seemed to make much of a difference.  ifconfig shows that there are 5 (out 
of 600K+) dropped RX packets on only 1 of the 2 bridged interfaces.  All of the other error-indicating counters are 0.  
Again, system resources remain low when the system is inline.  So I don't know that performance is really an issue. 
Using daq 2.0.2 because that's what's avilable in Gentoo's software repository.  If/when 2.0.4 becomes available, I'll 
upgrade and see if it makes a difference.
I suspect that snort is dropping random packets, but have no way to confirm.
Thanks for the response YM, Still hoping for some useful advice from the community.


# I see. Have you also disabled lro, gro, and the rest of the gang? They have been the most part of the issue when 
setting up Snort inline. And while you are at the NIC level, you may also want to adjust RX/TX buffers.
Another thing that I would tune in specific is the http_inspect preprocessor, and then move to the remaining 
configurations, like disabling unwanted preprocessors and rules..Hope this can helps.
YM


Date: Wed, 12 Nov 2014 20:31:31 -0800
From: charles.heselton () gmail com
To: snort-users () lists sourceforge net
Subject: [Snort-users] Inline snort negative impact on network

I'm attempting to install/configure a standalone, inline snort box.  When I have the sensor inline, with snort running, 
the traffic seems to be flowing properly; snort is alerting, as expected.  
However, browsing the web, and downloads, becomes significantly impacted.  speedtest.net fails to load.  wget downloads 
files at ~6Kbps, when it should be closer to 6Mbps.
The question is why?
Hardware:  Intel Celeron 4 core, 8GB RAM, 64GB SSD, dual Gigabit (Realtek) NICs onboard, USB3.0->Gigabit dongle NIC 
(for admin).
Software:  Gentoo x86_64 linux; kernel 3.16.5; snort 2.7.0; daq 2.0.2.
When snort is running, and traffic is passing, both gkrellm and top show almost 0 CPU activity.  This is on a 
relatively low traffic, home network, so I wouldn't expect the system to be loaded.  The admin interface shows more 
activity than the 2 bridged interfaces.
What gives?  Any advice appreciated.
Thanks,Charlie




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