Using more than one firewall

Hello.
I have a general question about firewalls. In most cases, is it alright to use more than one firewall? Can they interfere with each other, and cause security risks? Is it recommended to use only one firewall, or is it case-specific?
I am using Sygate and ZoneAlarm on Windows 98SE, but I have been told that this is not ok. On my Linux system, I am using the firewall that came with RedHat.
Thank you.
-Julien

I see no point to using more than one firwall because the first one will block the incoming connection before it even gets to the second firewall ... if you have one firewall installed and have it configure _properly_ then using 2 is pointless :)

Using several software firewalls on the same machine is asking for trouble. They may interfere with each other, and prevent each other from updating properly etc.

Using a software firewall combined with either a hardware firewall or a dedicated firewall device on generic hardware, is fine.

As far as I'm aware, Linux firewalls either just use iptables to implement the filtering, or in the case of expensive commercial solutions, bypass the kernel's IP stack entirely and implement their own. Either way, you won't want to put multiple ones on, they will just wrestle for control of the kernel's iptables.

Slarty

Thank you slarty, this is what I wanted to know.

Just to point out that there is a school of thought that once you have a properly configuerd hardware firewall a software firewall is surplus to requirements and a waste of system reasorces. The greater the number of services running on a machine the less secure the machine becomes.

I think that good idea is to read Sygate forum:
http://forums.sygate.com/vb/showthre...ther+firewalls
Can Sygate Firewall coexist with other firewalls?
Products:
Sygate® Personal Firewall STD
Sygate® Personal Firewall Pro
Operating systems:
All supported operating systems.

Details:
No, Sygate® Personal Firewall STD and Sygate® Personal Firewall Pro will not function while another firewall are running. In order to properly run SPF you will need to uninstall any other software firewalls prior to installing SPF

Keywords:
Firewall, ICF, ZoneAlarm, Norton, BlackICE, Agnitum Outpost,