The Bimap Rule: Performing Two-Way Translations; Figure 8-10 Nat Rule: Add (Bimap Flavor) - ZyXEL Communications Prestige 623 series User Manual

Prestige 623 Series Dual-link ADSL Router

8.6.5 The Bimap Rule: Performing Two-way Translations

Unlike the other NAT flavors, the bimap flavor performs address translations in both the outgoing and
incoming directions.
In the incoming direction, when the specified Prestige interface receives a packet with your public IP
address as the destination address, this address is translated to the private IP address of a computer on your
LAN. To the external computer, it appears as if the access is being made to the public IP address, when, in
fact, it is communicating with a LAN computer.
In the outgoing direction, the private source IP address in a data packet is translated to the LAN's public IP
address. To the rest of the Internet, it appears as if the data packet originated from the public IP address.
Bimap rules can be used to provide external access to a LAN device. They do not provide the same level of
security as rdr rules, because rdr rules also reroute incoming packets based on the port ID. Bimap rules do
not account for the port number, and therefore allow external access regardless of the destination port type
specified in the incoming packet.
To add a bimap rule, follow these instructions:
Step 1.
Display the NAT Rule – Add Page, choose a Rule ID, and select BIMAP from the Rule
Flavor drop-down list menu.
Step 2.
Select the interface and, if desired, a protocol that this rule applies to.
Step 3. In the Local Address field, type the private IP address of the computer to which you are
granting external access.
Step 4. In the Global Address field, type the address that you want to serve as the publicly known
address for the LAN computer.
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Figure 8-10 NAT Rule: Add (BIMAP flavor)

Configuring Network Address Translation