I have a private Class C network set up with a Linux firewall separating it from a public Class A network. The IP on eth0 is 207.247.227.1 and eth1 is 10.1.100.1 I can ping everywhere I need to (the 207 to the 10.1.100.* and the 10.*.*.* to anywhere on 207.247.227.*) but I can't ping from 207.247.227.* to 10.1.5.* I'm pretty new to this and I've been reading up on subnetting and classes. It seems to me that I should be able to do route add -net 207.247.227.0 gw 10.0.0.0 netmask 255.255.255.0 to hit it, but to no avail. I've tried variations on this and I think that there is something I'm simply not grasping. If anyone can help, thank you!!!

Brrrr.... 10.0.0.0 can not have 255.255.255.0 netmask, if it is not a CIDR network. I have no ideas about your network topology, but if the problem is only to ping from 207.247.227.* to 10.1.5.* , check the gateway routing table to/from this networks, and also try to traceroute packages to handle the problem with routing.

well as NetPortal pointed out, you may have mixed up netmasks and private/public address ranges. - Class A - 1st byte Address range 1 - 126 default mask 255.0.0.0 - Class B - 1st byte Address range 128 - 191 default mask 255.255.0.0 - Class C - 1st byte Address range 192 - 223 default mask 255.255.255.0 IP address space for private internal networks: 10.0.0.0 - 10.255.255.255 172.16.0.0 - 172.31.255.255 192.168.0.0 - 192.168.255.255 This private address range will not be routed in the Internet. Do you use masquerading on your firewall ? It's a special kind of network address translation used to connect private internal networks with the internet.