[Bro] High cpu when calling lookup_hostname

Pasqualino Paladino pasqualino.paladino at gmail.com
Fri May 6 03:16:34 PDT 2016

Hello everybody,

I’m using Bro 2.4.1 stable and I developed a script in order to add some
information to http.log.

This code snippet attempts to lookup each external hostname that is being
contacted by an internal IP.

*                                            if(c?$http && c$http?$host &&
c$http$host != ""){*

*                                                           when (local h =

if (|h|>0 && ( !in h))*


c$http$host_ip = h;*

Log::write(HTTP::LOG, c$http);*



*                                                           }*

*                                                           timeout 2 sec {*


*                                                           }*

*                                            }*

My problem is that the cores that have been assigned for Bro are using the
100% of the cpu and I guess the problem is caused by *when* call.

I have tried to install an internal dns cache (Bind9) in order to increase
the performance, but, having a 300 mb/s of throughput and setting 2 sec of
timeout doesn’t work .

By disabling the script bro has the expected behavior (around 50%-60% of
cpu usage).

Is anyone able to help me?

Thanks in advance,

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