Setting Up NAT with Multihoming

Multihoming enables a server to have multiple IP addresses. Multihoming can be achieved by adding a secondary IP address to an existing interface or by physically adding another interface to the server and binding another IP address to it.

A secondary IP address added to an existing interface must be on the same network as the IP address already bound to that interface. If there are multiple interfaces and the secondary IP address being added is not valid on any of the existing networks, the address is rejected and an error message appears on the server console.

For example, if the IP addresses 130.57.0.1 and 10.0.0.1 are bound to two interfaces and you attempt to add 172.16.1.1 as a secondary IP address, it will be rejected because it does not belong to the same network as 130.57.0.1 or 10.0.0.1.

Multihoming is required for NAT when static mode is used.

For an example of using multihoming with NAT, refer to the NAT online documentation. For information about how to set up NAT for a particular implementation with Proxy Services or the Virtual Private Network (VPN), refer to the Setting Up Proxy Services or Upgrading Virtual Private Networks.

When multihoming is used with a proxy server, a VPN, NAT, or any other TCP/IP application, an administrator must configure secondary addresses from the server console.

To configure secondary IP addresses for multihoming, complete the following steps:

1. At the server console, enter

   LOAD INETCFG

2. Select Protocols.

3. If TCP/IP was not configured on the public interface during installation, enable TCP/IP under Protocols, then bind one IP address to the public interface under Bindings.

4. Press Esc until you are prompted to save your changes and select Yes.

5. Select Manage Configuration and Edit autoexec.ncf.

6. Add a secondary IP address by entering the following command after the line that executes INITSYS.NCF:

   ADD SECONDARY IPADDRESS n.n.n.n

   where n.n.n.n is your server's secondary IP address.

   IMPORTANT:  This command will not take effect until the system is restarted. For this command to take effect immediately, enter the command at the server console.

7. To delete or display secondary IP addresses, press Alt+Esc until the server console prompt is displayed.

   • You can delete secondary IP addresses by entering the following command:

   DELETE SECONDARY IP ADDRESS n.n.n.n

   where n.n.n.n is your server's secondary IP address.

   • Ensure that when you delete secondary IP addresses, the corresponding commands are also removed from AUTOEXEC.NCF.

   You can display secondary IP addresses by entering the following command:

   DISPLAY SECONDARY IP ADDRESS