Date: Wed, 29 Jan 2014 15:31:12 +0100 From: Fabian Wenk <fabian@wenks.ch> To: freebsd-security@freebsd.org Subject: Re: portscans and blackhole Message-ID: <52E910B0.4030606@wenks.ch> In-Reply-To: <52DD08F7.1000306@hfbk-hamburg.de> References: <52DD08F7.1000306@hfbk-hamburg.de>
next in thread | previous in thread | raw e-mail | index | archive | help
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=1
>
> 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[=[0 | 1 | 2]]
sysctl net.inet.udp.blackhole[=[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 “Connection refused”. 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=2, or even
with UDP packets, then also set net.inet.udp.blackhole=1.
What output does 'sysctl -a | grep blackhole' show?
bye
Fabian
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?52E910B0.4030606>