[CentOS] CentOS 6.3 as Firewall/Router

Tim Evans tkevans at tkevans.com
Fri Jan 4 21:04:52 UTC 2013

On 01/04/2013 03:03 PM, Dale Dellutri wrote:
> On Fri, Jan 4, 2013 at 11:01 AM, Tim Evans <tkevans at tkevans.com> wrote:
>> I'm replacing an ancient Solaris 'ipf' firewall/router with a brand new
>> CentOS 6.3 system.  In the olden days, I successfully used the attached
>> iptables script (as /etc/rc.local) on Red Hat 5.x systems, but this doesn't
>> seem to be quite working on the new system.
>> Specifically, while it seems to be routing ok, you cannot connect to
>> anything on the inside net (e.g., with ssh or a browser) and cannot connect
>> to the system with ssh or anything else from elsewhere on the inside net.
>> Yet arp shows this system active.
>> Is there obsolete stuff here, and/or anything missing that would cause this?
> You found the error, but I have a question about running this in rc.local.
> Aren't you opening a very short time security hole by running this from
> rc.local?  Service network starts up early in the startup sequence
> (/etc/rc.d/rc3.d/S10network), and rc.local is at the very end.
> Wouldn't it be better to run the iptables rules once, then do:
>    service iptables save
> This way, iptables rules would be in place (S08iptables) before
> netowrk startup.

Thanks, Dale.  I'm trying to remember why I did it this way (nearly 10 
years ago, when I did this first.)  Seems it had to do with not turning 
on routing until the very end (instead of enabling it in 
/etc/sysctl.conf), relying on the out-of-the-box iptables rules in the 
interim (iptables still starts normally). This script overlays its 
rules, then turns on NAT and routing.

Tim Evans			|   5 Chestnut Court
UNIX System Admin Consulting	|   Owings Mills, MD 21117
http://www.tkevans.com/		|   443-394-3864
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