Example: Configuring Destination NAT for Single Address Translation

This example describes how to configure a destination NAT mapping of a single public address to a private address.

Note: Mapping one destination IP address to another can also be accomplished with static NAT. Static NAT mapping allows connections to be established from either side of the gateway device, whereas destination NAT only allows connections to be established from one side. However, static NAT only allows translations from one address to another or between blocks of addresses of the same size.

Requirements

1. Configure network interfaces on the device. See the Junos OS Interfaces Configuration Guide for Security Devices .
2. Create security zones and assign interfaces to them. See Understanding Security Zones.

Overview

This example uses the trust security zone for the private address space and the untrust security zone for the public address space. In Figure 1, devices in the untrust zone access a server in the trust zone by way of public address 1.1.1.200/32. For packets that enter the Juniper Networks security device from the untrust zone with the destination IP address 1.1.1.200/32, the destination IP address is translated to the private address 192.168.1.200/32.

Figure 1: Destination NAT Single Address Translation

• Destination NAT pool dst-nat-pool-1 that contains the IP address 192.168.1.200/32.
• Destination NAT rule set rs1 with rule r1 to match packets received from the ge-0/0/0.0 interface with the destination IP address 1.1.1.200/32. For matching packets, the destination address is translated to the address in the dst-nat-pool-1 pool.
• Proxy ARP for the address 1.1.1.200/32 on interface ge-0/0/0.0. This allows the Juniper Networks security device to respond to ARP requests received on the interface for that address.
• Security policies to permit traffic from the untrust zone to the translated destination IP address in the trust zone.

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Step-by-Step Procedure

1. Create the destination NAT pool.
   [edit security nat destination]user@host# set pool dst-nat-pool-1 address 192.168.1.200/32
2. Create a destination NAT rule set.
   [edit security nat destination]user@host# set rule-set rs1 from interface ge-0/0/0.0
3. Configure a rule that matches packets and translates the destination address to the address in the pool.
   [edit security nat destination]user@host# set rule-set rs1 rule r1 match destination-address 1.1.1.200/32user@host# set rule-set rs1 rule r1 then destination-nat pool dst-nat-pool-1
4. Configure proxy ARP.
   [edit security nat]user@host# set proxy-arp interface ge-0/0/0.0 address 1.1.1.200/32
5. Configure an address in the global address book.
   [edit security address-book global]user@host# set address server-1 192.168.1.200/32
6. Configure a security policy that allows traffic from the untrust zone to the server in the trust zone.
   [edit security policies from-zone untrust to-zone trust]user@host# set policy server-access match source-address any destination-address server-1 application anyuser@host# set policy server-access then permit

Results

From configuration mode, confirm your configuration by entering the show security nat and show security policies commands. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.

If you are done configuring the device, enter commit from configuration mode.

Verification

To confirm that the configuration is working properly, perform these tasks:

• Verifying Destination NAT Pool Usage
• Verifying Destination NAT Rule Usage
• Verifying NAT Application to Traffic

Verifying Destination NAT Pool Usage

Purpose

Verify that there is traffic using IP addresses from the destination NAT pool.

Action

From operational mode, enter the show security nat destination pool all command. View the Translation hits field to check for traffic using IP addresses from the pool.

Verifying Destination NAT Rule Usage

Purpose

Verify that there is traffic matching the destination NAT rule.

Action

From operational mode, enter the show security nat destination rule all command. View the Translation hits field to check for traffic that matches the rule.

Verifying NAT Application to Traffic

Purpose

Verify that NAT is being applied to the specified traffic.

Action

From operational mode, enter the show security flow session command.