What's wrong with this iptables syntax??

registering · 06-16-2004, 08:38 AM

Hi all!
My firewall's working fine, except it seems that packets originating on the firewalled-server itself are not being forwarded. So if packets arrive AT the server going to A, they get properly sent to B, but if packets originating ON the server go to A, they don't get sent anywhere. I'm using iptables v 1.2.9 on SUSE 9.1 Pro. As far as I can tell from the man pages, this command below is valid, but I always get an "invalid argument" when I execute it:

Code:

iptables -t nat -A OUTPUT -d 1.2.3.4 -j DNAT --to-destination 192.168.0.5

Any ideas what's wrong with the above? The only other rules for OUTPUT are:

Code:

iptables -P OUTPUT ACCEPT
iptables -F OUTPUT

nukkel · 06-16-2004, 02:53 PM

Could you send the exact error message?
This command should normally execute successfully...

demian · 06-16-2004, 03:12 PM

The syntax is correct. However, for this command to work you need to set the parameter CONFIG_IP_NF_NAT_LOCAL during kernel configuration.

I think some distribution kernels don't include this options in their pre-compiled kernels since NAT'ing locally generated connections is a somewhat unusual thing to do: After all when the connection is generated on the local machine why not make it a connection with the "right" destitination in the first place?

registering · 06-16-2004, 03:54 PM

Thanks! That explains it. What was happening is, I have a DNS on A and a web server on B. To enable everyone to access B (internal and external folks), the DNS gives a global ip address, then uses a firewall to route the packets to B. Thus, if a user is ON A and surfs to the web server, DNS gives it a global ip address, and the packets weren't routing since the packets were originated from A. However I've since changed this so my DNS serves-up different addresses based on who's asking (using the "view" tag). So you're right, now that I made my DNS better, there's no need for this rule.

But I appreciate the help!