Can't connect local network to internet.

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http://forums.fedoraforum.org – I have been doing this for years, but was using a very old (Redhat 9!) system for the gatewey. As it's failing, I'm trying to configure an F17 system for the same purpose. Where I'm stuck: System A has 2 interfaces. I have disabled NetworkManager as it complicated things too much. Outside world interface: (/etc/sysconfig/network-scripts/ifcfg-p3p1) UUID="347ac2ad-0fc9-4170-a215-8bd9a1cfa5e1" NM_CONTROLLED="no" BOOTPROTO="dhcp" DEVICE="p3p1" ONBOOT=yes TYPE=Ethernet DEFROUTE=yes IPV4_FAILURE_FATAL=no IPV6INIT=no NAME="System p3p1" HWADDR=00 (HowTos)