FreeBSD 7, bridge, PF and syn flood = very bad performance

Stefan Lambrev stefan.lambrev at moneybookers.com
Sat Jan 26 13:00:04 PST 2008


Max Laier wrote:
> On Friday 25 January 2008, Stefan Lambrev wrote:
>   
>> Greetings,
>>
>> Does anyone try to see PF with "keep state" in action when under syn
>> flood attack?
>> I tried to get some help in freebsd-pf@, because the test firewall,
>> that I build hardly can handle 2-5MB/s syn flood.
>> Unfortunately I do not saw useful advice.
>> The problem is that a quad core bridge firewall running freebsd 7 amd64
>> with PF is near useless and can't handle "small" SYN ddos.
>>
>> Here is the schema that I'm testing:
>> web server (freebsd) - freebsd (bridged interfaces) - gigabit switch -
>> clients + flooders
>> In this configuration ~25MB/s syn flood (and I think this limit is
>> because of my switch) is not a problem and the web server responds
>> without a problem.
>> With this configuration netperf -l 610 -p 10303 -H 10.3.3.1 shows
>> 116MB/s stable speed , so I guess there are no problems with cables,
>> hardware and etc :)
>>
>> But when I start pf (see below the config file) the traffic drops to
>> 2-3MB/s and the web server is hardly accessible.
>> It seems that device polling helps a lot in this situation, and at
>> least the bridge firewall is accessible. Without "polling" the firewall
>> is so heavily loaded
>> that even commands like "date" take few seconds to finish, with 2 cores
>> at ~100% idle at same time.
>>
>> I have "flat profiles" from hwpmc, and I think it indicates a problem:
>>
>> (bridge, pf enabled, polling enabled, sched_ule - I have profiles and
>> for other combinations too if needed)
>>   %   cumulative   self              self     total
>>  time   seconds   seconds    calls  ms/call  ms/call  name
>>  24.0  268416.00 268416.00        0  100.00%           _mtx_lock_sleep
>>     
>
> Can you build a kernel with LOCK_PROFILING and try to figure out which 
> lock is causing this?
>   
Yes I can build kernel with LOCK_PROFILING.
But I have no idea how to use it :)
Can you point me to some documentation?



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