Two NIC Routing Question

[Michael Mansour]

Hi Jake,

> I have a class two NIC firewall.  eth0 is my external interface 
> connected to my cablemodem, eth1 is my internal interface connected 
> to my hub.  I am using iptables-based firewall rules and using NAT 
> so I can access the internet from all my desktops.  Everything is 
> working correctly.
> 
> The problem is that it only works if I manually set up a default gateway
> route through the external interface.  After I boot the system, I 
> type the following command:
> 
>    route add default gw x.x.x.x
> 
> where x.x.x.x is the address assigned to my external interface. If I 
> don't do this, I cannot access anything on the internet from any my 
> internal machines. Once I execute this command it all works as 
> expected.  I am certain, however, that as a RH 7.2 system, which is 
> what I was before I started incrementally upgrading to FC1 where I 
> am now, I did not need to do this for it to work.
> 
> How can I get this routing between two NICs to work correctly without
> manually executing a 'route' command?  Please don't tell me to add this
> command to rc.local.  My external IP address is dynamic so it can change
> between reboots.  I need some mechanism that works dynamically.  I'm 
> sure that it used to work this way!

I was actually surprised to find that out of so many replies to you, people
seemed to have missed the answer to your problem.

In your /etc/sysconfig/network-scripts/ifcfg-ppp0 file, this is the file
that's used to configure your link/routing when you dialup. There's a variable
here you need to set:

DEFROUTE=yes

which will grab the default route information from your ISP and configure your
routing for you. For this to work, you should _not_ set a GATEWAY variable in
your /etc/sysconfig/network file. The GATEWAY flag adds a static default route
to your routing table on system boot, which is not what you want in your
situation. Within the /etc/sysconfig/network file remove the GATEWAY flag (if
it's in there) and add:

GATEWAYDEV="ppp0"

which will tell the rc network script to use the default route supplied by the
ifcfg-ppp0 script which picks that up from your ISP.

Other interesting variables you can use in ifcfg-ppp0 are:

ONBOOT
PEERDNS
CLAMPMSS
FIREWALL

there's docs in the system somewhere (I forgot where I read all this when
first doing it) which explains what each variable does, you should review it
to allow you to better understand how the process works.

Regards,

Michael.