I can't find this one in any previous posts.

I am trying to set up a Linux box (under RedHat 7) to function as a firewall server for my network and communicate out via a cable modem. It works, except...

I have the thing running DHCP for the modem interface (eth1), and a static address for the internal side (eth0). When I first boot up the system all is well - my other machine can see out and browse OK. Unfortunately after about an hour (roughly), eth1 seems to just lose its IP address (no errors reported), and of course IP forwarding then fails. eth1 still claims to be up in ifconfig, but it has no address assigned.

I know the modem is OK, because it functions without a hitch on my windows machine. Any ideas where to look for a fix?

Thanks.

ah. Linux has problems with DHCP (as if anyone else gets it right 8)

You need to kill dhcpcd every hour or so and restart it. You can do this with a shell script and a crontab

dhcpcd_update:
#!/bin/sh

myvar = $(ps -C dhcpcd -o pid=)

if [ $myvar ]; then
kill $myvar
else
echo "no dhcpcd started"
fi

/sbin/dhcpcd -d > newip.out

# do whatever you want to with newip.out here

crontab:
I can't find the file, so man crontab will explain things. These are my settings (2 hr intervals) My DSL is rock solid when SWBell decides not to drop my connection.

0 */2 * * * /root/dhcpcd_update 1> /dev/null 2> /dev/null

Er, my system isn't running dhcpcd, even when it works...?

Wait a minute...

It is correct that your system isn't running dhcpd (dhcp server). Your system is a dhcp client. The cable (modem) company is running a dhcp server to assign a ip-address to interface (eth1).

I don't know the solution for the problem.
It seems like the lease time expires and the ip-address is not reassigned. Try to find out what the lease time is.

JS.

Which provider are you going through?

I am running the same setup as you, redhat 7 through bigpond cable, with firewall rules, and have no probs.