Default installation of firewall in Linux-how to check for one

achtung_linux · 08-26-2006, 11:36 AM

Hi,
I was wondering if any Linux installation comes with firewall that installs by default. If not, how to check if one exists on local Linux machine?
I have a simple network made of a box under CentOS 4.2 and another under WinXP Home, and am unable to get a simple VoIP softphone to register with a server on my CentOS box (also CentOS is invisible in My Network Neighbourhood on WinXP box, but samba succesfully downloads from WinXP). I suspect firewall stands in the way, but I don't know how to check for one on Linux...

win32sux · 08-26-2006, 07:26 PM

Quote:

Originally Posted by achtung_linux

Hi,
I was wondering if any Linux installation comes with firewall that installs by default. If not, how to check if one exists on local Linux machine?
I have a simple network made of a box under CentOS 4.2 and another under WinXP Home, and am unable to get a simple VoIP softphone to register with a server on my CentOS box (also CentOS is invisible in My Network Neighbourhood on WinXP box, but samba succesfully downloads from WinXP). I suspect firewall stands in the way, but I don't know how to check for one on Linux...

almost all linux distros come with a firewall... the firewall is called netfilter (it's part of the kernel), and the tool to configure it is called iptables...

http://www.netfilter.org/

having said that, i should point out that many distros leave the iptables default configuration after an install (which happens to be the equivalent of having the firewall disabled)... those distros expect one to configure it according to one's needs post-install... an example of distros that do this could be Ubuntu and Slackware...

you can check your firewall's configuration by executing this command (as root):

Code:

iptables -L -n -v

post the output of the command if you want help interpreting it...