Example: Configuring Destination NAT for IP Address and Port Translation

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 servers in the trust zone by way of public address 1.1.1.200 on port 80 or 8000. Packets entering the Juniper Networks security device from the untrust zone are mapped to the private addresses of the servers as follows:

• The destination IP address 1.1.1.200 and port 80 is translated to the private address 192.168.1.200 and port 80.
• The destination IP address 1.1.1.200 and port 8000 is translated to the private address 192.168.1.220 and port 8000.

Figure 1: Destination NAT Address and Port Translation

• Destination NAT pool dst-nat-pool-1 that contains the IP address 192.168.1.200 port 80.
• Destination NAT pool dst-nat-pool-2 that contains the IP address 192.168.1.220 and port 8000.
• Destination NAT rule set rs1 with rule r1 to match packets received from the untrust zone with the destination IP address 1.1.1.200 and destination port 80. For matching packets, the destination address is translated to the address in the dst-nat-pool-1 pool.
• Destination NAT rule set rs1 with rule r2 to match packets received from the untrust zone with the destination IP address 1.1.1.200 and destination port 8000. For matching packets, the destination IP address and port are translated to the address and port in the dst-nat-pool-2 pool.
• Proxy ARP for the address 1.1.1.200/32. 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 addresses 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 destination NAT pools.
   [edit security nat destination]user@host# set pool dst-nat-pool-1 address 192.168.1.200 port 80user@host# set pool dst-nat-pool-2 address 192.168.1.220 port 8000
2. Create a destination NAT rule set.
   [edit security nat destination]user@host# set rule-set rs1 from zone untrust
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 1.1.1.200user@host# set rule-set rs1 rule r1 match destination-port 80user@host# set rule-set rs1 rule r1 then destination-nat pool dst-nat-pool-1
4. 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 r2 match destination-address 1.1.1.200user@host# set rule-set rs1 rule r2 match destination-port 8000user@host# set rule-set rs1 rule r2 then destination-nat pool dst-nat-pool-2
5. Configure proxy ARP.
   [edit security nat]user@host# set proxy-arp interface ge-0/0/0.0 address 1.1.1.200/32
6. Configure addresses in the global address book.
   [edit security address-book global]user@host# set address server-2 192.168.1.220/32 user@host# set address server-1 192.168.1.200/32
7. Configure a security policy that allows traffic from the untrust zone to the servers 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 server-2] 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.