Re: portscans and blackhole

Hello

On 20.01.14 12:31, sa9k063 wrote:
> can someone please explain:
>
> one of my boxes gets portscanned often by some likely infected laptops.
> While having set
>
> net.inet.tcp.blackhole=3D1
>
> there are still messages like
>
> +Limiting closed port RST response from 348 to 200 packets/sec

According to the blackhole(4) manpage (from a FreeBSD 9.1 system):

---8<------------------------------------------------------------
SYNOPSIS
      sysctl net.inet.tcp.blackhole[=3D[0 | 1 | 2]]
      sysctl net.inet.udp.blackhole[=3D[0 | 1]]

Part of DESCRIPTION:
Normal behaviour, when a TCP SYN segment is received on a port =

where there is no socket accepting connections, is for the system =

to return a RST segment, and drop the connection.  The connecting =

system will see this as a =93Connection refused=94.  By setting the =

TCP blackhole MIB to a numeric value of one, the incoming SYN =

segment is merely dropped, and no RST is sent, making the system =

appear as a blackhole.  By setting the MIB value to two, any =

segment arriving on a closed port is dropped without returning a =

RST.  This provides some degree of protection against stealth =

port scans.
---8<------------------------------------------------------------

So it is possible, that you are hit with something else then SYN =

packets and should probably set net.inet.tcp.blackhole=3D2, or even =

with UDP packets, then also set net.inet.udp.blackhole=3D1.

What output does 'sysctl -a | grep blackhole' show?


bye
Fabian
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