Linux IP Masquerade HOWTO

Chapter 5. Testing IP Masquerade

Finally, it's time to give IP Masquerading an official try after all this hard work. If you haven't already rebooted your Linux box, do so to make sure the machines boots ok, executes the /etc/rc.d/rc.firewall-* ruleset, etc. Next, make sure that both the internal LAN connection and connection of your Linux hosts to the Internet is okay.

Follow these -11- tests to make sure all aspects of your MASQ setup is running properly:

5.1. Loading up the rc.firewall ruleset

Step One: run the correct firewall for your machine via command "/etc/rc.d/rc.firewall-[iptables / ipchains /ipfwadm]". For example, Linux 2.6 users would run "/etc/rc.d/rc.firewall-iptables"

Does it load with some strange errors? Here are some exmaples and help to fix them:

Problem #1:
```
ip_tables, Using /lib/modules/2.4.2-2/kernel/net/ipv4/netfilter/ip_tables.o
/lib/modules/2.4.2-2/kernel/net/ipv4/netfilter/ip_tables.o: init_module: Device
or resource busy
Hint: insmod errors can be caused by incorrect module parameters, including
invalid IO or IRQ parameters
    
```
Run the command "/sbin/lsmod" and make sure the module "ipchains.o" is NOT installed. If it is installed, your machine (most likely Redhat-7.x based) is probably trying to load an IPCHAINS ruleset which is incompatible with IPTABLES.
To disable this from happening in the future, run the command:
```
   chkconfig --level=2345 ipchains off
   
```
To remove the "ipchains" module without rebooting, run the command:
```
   /sbin/rmmod ipchains
   
```
and the re-try to load the rc.firewall-* ruleset.
Problem #2:
```
    .
    .
    Creating a DROP chain..
    iptables v1.2.3: log-level `info' ambiguous
    .
    .
    
```
Your version of IPTABLES it too old. You need to upgrade it with a newer version via an updated RPM, DEB, or via compiling up the source. You can get an updated version from your Linux distribution manufacturer or from the NetFilter WWW site. This is all covered in the Section 2.6 section.
Problem #3:
```
    No such file: 
         
```
Did you copy this rc.firewall-* file from a DOS machine? Load the rc.firewall-* file in a binary editor such as ViM (vim -b /etc/rc.d/rc.firewall-*) and make sure that every line is NOT finished with a ^M.