I'm trying to configure a Mac OS X box with two NICs as a router complete with DHCP and NAT which in theory shouldn't be too much of a challenge but at the moment I'm learning theory and reality are rather different.
I have en0 connected to the internet and en1 connected to LAN. Using the server utility I have only DHCP and NAT enabled. I have configured a subnet complete with DNS, search domains, etc. The NAT tab has ethernet 1 (en0) set for IP forwarding and NAT.
Clients are able to connect to the network via an access point and are being served DHCP addresses complete with DNS and search domains via the machine however any clients are unable to access the internet on port 80 or ping anything outside but we are able to ping devices within the lan just fine.
I'm sure there's more details that I'm missing so you can also find a complete plist dump from server utility here.
Edit: Forgot to mention that this is Mac OS 10.5