Network Adapters, IP Addresses and Firewall Zones

openSUSE 11.0: A short overview how I configured the network devices and the firewall

This article and covers the configuration of the openSUSE 11.x firewall.

Rule # 1: Pay attention to IP Address conflicts. If the address is already used by another device, the configuration may be ok, but it still doesn't work. Of course everybody knows that, just wanted to throw this one in ... for 'almost' no reason :-)

Note: 11.1 version and earlier version may have an issue with the ethernet driver (e1000e).

Hardware configuration is as follows:
Network device built on the motherboard plus two 10/100 adapters. That's three adapters, one for the public Internet, one for my internal network and the third for my servers that require access from both, the Internet and internal network. One PC has 512MB+ memory, 6GB+ disk and a Pentium 4 2GHz+ processor. The PC uses less then 30 watts. Because all my system are on a UPS, the power consumption really matters - not only for environmental reasons.

IPv6 Support?
In YaST2 to to Network Devices > Network Settings then to to Global Options, I unchecked the Enable IPv6 option. I don't use this yet and the Administration Document mentions that there is less overhead when disabled.

DHCP or not?
I don't use DHCP at all. If I do need the function, I'll power up my $20 Netgear Router, it does a fine job.

Firewall Zone in the Device Configuration
I also changed the Firewall Zone from Automatically Assign Zone to the correct zone. This is in YaST2 then goto Network Devices > Network Settings then goto Overview. Edit each Controller the General tab and select the correct zone if not already set.

Minor Problem (bug?) with adapter configuration: (fixed in 11.3)
When adding a new IP address to the external zone, I was not able to remove the address again. I can change, but not remove. I had to manually configure the file.
1. stop the network with rcnetwork stop
2. edit the /etc/sysconfig/network/ifcfg-eth2 and comment the line pairs with IPADDR_xx and LABEL_xx. Also commented the PREFIXLEN-xx lines.
3. save the file and restart the network with rcnetwork start
Now the configuration shows correctly in YaST and the firewall.

The final setup is as follows:
External Zone: about 10 IP Addresses all in the 207.176.something range
Internal Zone: the network with all my desktops
Demilitarized Zone: the network with my webserver(s).

In the firewall configuration, this is the basic setup.
Open YaST2 and go to Securty and Users > Firewall

Start-Up is not much to change
Interfaces shows my 3 network devices plus the any interface.
Allowed Services has the generic ports by zone that are needed to keep the PC working. More details below.
Masquerading has to bulk of the configuration. All the IP address, port and protocol forwarding rules are here.
Broadcast no change
IPsec Support no change
Logging Level no change
Custom Rules no change

Allowed Services configuration
When I checked the Protect Firewall from Internal Zone, I was not able to get the desktop PCs on the Internal Zone to work correctly. Eventually I just left it unchecked ... for now.
I added some services to the allow list for the Demilitarized Zone, such as DNS, SMTP, HTTP, HTTPS, Lotus Domino and some more.
I added no ports to the allow list for the External Zone.
No need to add anything on the Internal Zone since I didn't check the Protect Firewall from Internal Zone

To handle multiple IP addresses from the external Zone, I added several Masquerading entries.
I'm adding one entry per redirect and port and protocol. The source network is usually 0/0 for my purpose, the requested IP is which I redirect to

These are the major configuration changes and all works fine up to this point.

Update / Revision: January 3 2009
No problems with the firewall. I made major configuration changes to simplify my DNS entries and consequently simplifying my Masquerading configuration.
Back in mid December, I configured a brand new system based on my instructions here. It worked without a problem. Once the setup was done and the firewall was working with different IP addresses and only a minimal firewall configuration, it was time to switch the hardware.
One night, I copied the configuration files to the new system:
etc/sysconfig/SuSEfirewall2 << this is the firewall configuration
etc/sysconfig/network/ifcfg-eth2 << this is the IP address configuration for the external network
the ifcfg-eth0 and ifcfg-eth1 config files have one entry, the and the, so no need to copy them as well.

Update / Revision: November 7, 2010
Just upgraded to openSUSE 11.3 without issues. No or very minimal changes to the firewall or installation. I was able to copy the configuration entries (not the complete file) from the previous SuSEfirewall2 file to the new one.

First published on October 03, 2008
Last revised on November 07, 2010

Timestamp: 06/25/2017 08:11:55 AM EDT [on srv7cps]
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