3Com Switch 8800 Family Firewall Module Configuration and Command Reference Guide

Troubleshooting NAT Configuration 91
Troubleshooting: if an external host can not access the internal server normally,
check the configuration on the internal server host, or the internal server
configuration on the security gateway. It is possible that the internal server IP
address is wrong, or that the firewall has inhibited the external host to access the
internal network. Use the command display acl for further check. Refer to
“Firewall Configuration”.