IPChains file? Where is it?

I am trying to set up a Masq environment on my LAN with my cable modem. I have a DHCP server running and successfully giving IP addresses to new computers on the LAN through 'eth1'. I have internet access working through 'eth0'. But I've noticed on boot that it says /sbin/ipchains is missing. (Which I hope explains why I cannot get outside internet access from 'eth1'. Which package needs to be installed to get ipchains on my system, or where can I download it? Thanks in advance for your assistance.