As well as having the gateway device setup as you have in /etc/sysconfig/network, I also like to make sure that the /etc/sysconfig/network-scripts/ifcfg-whatever configurations cannot be changed by setting the immutable bit as I found that webconfig tends to mess with them unexpectedly. Also, make sure the ifcfg-xxxx one for your wan has the gateway address specified. Example below. I also like to include the HWADDR so they cannot move around, especially when you have several identical NICs... Any strangeness in your /var/log/syswatch and /var/log/system logs, or even /var/log/messages for that matter, when the gateway is lost?