CLI: Example for Configuring Destination NAT for Internet Users to Access Intranet Servers (One-to-one Mappings Between Public Interfaces and Private IP Addresses)

This section provides an example for configuring destination NAT for Internet users to access intranet servers.

Networking Requirements

An enterprise has deployed a FW as a security gateway on the intranet border. Destination NAT is configured on the FW for the intranet File Transfer Protocol (FTP) servers to provide services for Internet users. The enterprise is allocated a public address 1.1.10.10 by an Internet service provider (ISP). In addition to the IP addresses of Internet interfaces, the enterprise applies for another public IP address (1.1.10.10) for the intranet server to provide services. Figure 1 illustrates the static mapping networking. The router is an access gateway on the ISP network.

Figure 1 Networking diagram for configuring destination NAT

Data Planning

Item		Data	Description
GigabitEthernet 0/0/1		IP address: 1.1.1.1/24 Security zone: Untrust	1.1.1.1/24 is a public address provided by the ISP.
GigabitEthernet 0/0/2		IP address: 10.2.0.1/24 Security zone: DMZ	Intranet servers use 10.2.0.1 as the default gateway address.
Destination NAT		Destination address pool: 10.2.0.7 to 10.2.0.8	When an Internet user accesses address 1.1.10.10, the FW that has the destination NAT function enabled can send traffic to the intranet server.
Routing information	Default route	Destination address: 0.0.0.0 Next hop address: 1.1.1.254	Configure a default route defined for the ISP router on the FW to direct intranet traffic to the router.

Configuration Roadmap

The configuration roadmap is as follows:

Assign IP addresses to interfaces, add the interfaces to security zones, and configure network connectivity.
Configure a security policy for traffic between Internet users and intranet servers.
Configure the destination NAT function so that when an Internet user accesses address 1.1.10.10‏, the FW can send traffic to the intranet server.
Configure a default route on the FW to direct intranet traffic to the ISP router.
Configure a blackhole route on the FW to prevent routing loops between the FW and router.
Configure static routes destined for public addresses of intranet servers on the router.

Procedure

Assign IP addresses to interfaces, add the interfaces to security zones, and configure network connectivity.

# Assign an IP address to GigabitEthernet 0/0/1.

<FW> system-view
[FW] interface GigabitEthernet 0/0/1
[FW-GigabitEthernet 0/0/1] ip address 1.1.1.1 24
[FW-GigabitEthernet 0/0/1] quit

# Assign an IP address to GigabitEthernet 0/0/2.

[FW] interface GigabitEthernet 0/0/2
[FW-GigabitEthernet 0/0/2] ip address 10.2.0.1 24
[FW-GigabitEthernet 0/0/2] quit

# Add GigabitEthernet 0/0/1 to the Untrust zone.

[FW] firewall zone untrust
[FW-zone-untrust] add interface GigabitEthernet 0/0/1
[FW-zone-untrust] quit

# Add GigabitEthernet 0/0/2 to the DMZ zone.

[FW] firewall zone dmz
[FW-zone-dmz] add interface GigabitEthernet 0/0/2
[FW-zone-dmz] quit

Configure a security policy for traffic between Internet users and intranet servers.

[FW] security-policy
[FW-policy-security] rule name policy1
[FW-policy-security-rule-policy1] source-zone untrust
[FW-policy-security-rule-policy1] destination-zone dmz
[FW-policy-security-rule-policy1] destination-address 10.2.0.0 24
[FW-policy-security-rule-policy1] action permit
[FW-policy-security-rule-policy1] quit
[FW-policy-security] quit

Configure a destination NAT address pool.

[FW] destination-nat address-group addressgroup1
[FW-dnat-address-group-addressgroup1] section 10.2.0.7 10.2.0.8
[FW-dnat-address-group-addressgroup1] quit

Configure a NAT policy.

[FW] nat-policy
[FW-policy-nat] rule name policy_nat1
[FW-policy-nat-rule-policy_nat1] source-zone untrust
[FW-policy-nat-rule-policy_nat1] destination-address 1.1.10.10 32
[FW-policy-nat-rule-policy_nat1] service protocol tcp destination-port  3000 to 3001
[FW-policy-nat-rule-policy_nat1] action destination-nat static port-to-address address-group addressgroup1 21
[FW-policy-nat-rule-policy_nat1] quit
[FW-policy-nat] quit

Configure black-hole routes destined to the destination address of traffic to prevent routing loops.
```
[FW] ip route-static 1.1.10.10 255.255.255.255 NULL0 
```

Enable NAT ALG for FTP.

[FW] firewall interzone dmz untrust
[FW-interzone-dmz-untrust] detect ftp
[FW-interzone-dmz-untrust] quit

Configure a default route to direct intranet traffic to the ISP router.
```
[FW] ip route-static 0.0.0.0 0.0.0.0 1.1.1.254
```
On the router, configure a static route, in which the destination address is 1.1.10.10 and the next-hop address is 1.1.1.1. The router directs traffic destined for 1.1.10.10 to the FW based on the static route so that the FW can forward the traffic to the intranet server.
Contact your ISP administrator to perform this step.

Configuration Scripts

Configuration script for the FW:

#
 sysname FW
#
interface GigabitEthernet0/0/1
 undo shutdown
 ip address 1.1.1.1 255.255.255.0 
#
interface GigabitEthernet0/0/2
 undo shutdown
 ip address 10.2.0.1 255.255.255.0 
#
firewall zone untrust
 set priority 5
 add interface GigabitEthernet0/0/1
#
firewall zone dmz
 set priority 50
 add interface GigabitEthernet0/0/2
# 
firewall interzone dmz untrust 
 detect ftp 
#
 ip route-static 0.0.0.0 0.0.0.0 1.1.1.254 
 ip route-static 1.1.10.10 255.255.255.255 NULL0 
# 
destination-nat address-group addressgroup1 0
 section 10.2.0.7 10.2.0.8 
#  
security-policy   
  rule name policy1  
    source-zone untrust 
    destination-zone dmz 
    destination-address 10.2.0.0 24 
    action permit 
#  
nat-policy  
  rule name policy_nat1 
    source-zone untrust 
    destination-address 1.1.10.10 32 
    service protocol tcp destination-port  3000 to 3001
    action destination-nat static port-to-address address-group addressgroup1 21
# 
return