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Transparent Mode Overview



Article ID: KB4160 KB Last Updated: 04 Jun 2010Version: 3.0
Transparent Mode Overview


Note: This article applies to ScreenOS 4.0 and higher.

In Transparent Mode, the NetScreen device operates as a Layer-2 bridge. The device inspects packets traversing the firewall without modifying any of the source or destination information in the IP packet header. Because it does not translate addresses, the IP addresses on the protected network must be valid, routable addresses on the Untrusted side of the network. In Transparent mode, the IP addresses for the V1-Trust security zone and V1-Untrust security zone are set at, making the presence of the NetScreen device invisible to the network. Firewall, VPN and traffic management are still enforced based on the policy set and configuration of the device.

  • IP addresses on the trust side include any routed networks before it reaches the NetScreen. For each subnet, configure an address book entry defining that subnet.
  • IP address of untrust hosts that need to communicate to internal systems are typically vendors or partners that need to communicate to specific hosts located on the internal network. Define an address book entry for this device on the untrust side.
  • Configure policies that explicitly define internal address book entries.
  • Avoid policies that allow widespread access to your network.

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