# Secondary IP Address Configuration

Each physical interface has a single, unique primary IP address. When it is necessary for an interface in the Trust or DMZ zone to have multiple IP addresses, you can add secondary IP addresses.

## Secondary Address Properties

Secondary addresses have certain properties that affect how you can implement such addresses.

- There can be no subnet address overlap between any two secondary IPs. In addition, there can be no subnet address overlap between a secondary IP and any existing subnet on the device.

- When you manage a device through a secondary IP address, the address always has the same management properties as the primary IP address. Consequently, you cannot specify a separate management configuration for the secondary IP address.

- You cannot configure a gateway for a secondary IP address.

- You cannot configure a secondary IP address in transparent mode. For example, if you configure the secondary IP in NAT or route mode and then attempt to change the mode to transparent mode, the action fails.

- Whenever you create a new secondary IP address, the device automatically creates a corresponding routing table entry. When you delete a secondary IP address, the device automatically deletes its routing table entry.

- Enabling or disabling routing between two secondary IP addresses causes no changes in the routing table. For example, if you disable routing between two such addresses, the device drops any packets directed from one interface to the other, but no changes occur in the routing table.

## Secondary IP Address List

At the top of the Interface (Secondary IPs) page, you can see which interface the secondary IP addresses belong to. For example, you see:

Interface: ethernet3/2 (IP/Netmask: 209.122.17.1/24)

This table lists all the secondary IP addresses that belong to the interface indicated at the top of the page.

IP Address/Netmask: Indicates the IP address and netmask.

Configure: Click Remove to remove the configure secondary IP address.

Note: You cannot modify a secondary IP address, but you can remove it, and then configure a new one.

### To Create a New Secondary IP

1. Enter the necessary information:

In the Add New Entry box, enter the IP address and the subnet mask of the secondary IP you are configuring.

2. Click Add to save the secondary IP address.

The new secondary IP address appears in the Secondary IP list.