Refers to the firewall's practice of concealing the IP addresses of hosts behind the firewall. For outbound traffic, the firewall, by default, substitutes its public IP address for the client's address in the source field of the packet. For inbound traffic, the firewall, by default, substitutes its private IP address for the client's address in the source field of the packet. Both of these practices can be changed by enabling client-side transparency on the firewall's outside and inside NICs, respectively. Due to routing restrictions, enabling client-side transparency on the firewall's outside NIC should never be done for those sites that use reserved addresses or illegal addresses behind the firewall.