DSL Modem and Linus Firewall

I have a Westall Versalink+ DSL modem, model D90-327-W15-06 Rev. G connected to a Cyberguard firewall which runs a version of Linux. From the modem, which is a modem/router, I can ping the directly connected interface on the firewall; but when I try to ping another interface also on the firewall ping fails. Traceroute shows the path going out the WAN side of the modem. I have defined a static route to the non-directly conncected firewall interface, but still cannot ping the non-directly connected interface on the firewall.

Does anyone have any suggestions?