[CentOS] CentOS 6.3 as Firewall/Router

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?

Thanks.