CLI: Example for Configuring NAPT and NAT Server for Internet Users to Access Intranet Servers

This section provides an example for configuring NAPT and NAT Server for Internet users to access intranet servers.

Networking Requirements

An enterprise has deployed a FW as a security gateway on the intranet border. Static mapping is configured on the FW for the intranet web and File Transfer Protocol (FTP) servers to provide services for Internet users. The enterprise is allocated a public address 1.1.1.10 by an Internet service provider (ISP). Public address 1.1.1.10 is mapped to the intranet server addresses. In addition, to hide addresses of public network users, source NAT policies are configured to translate source addresses. Figure 1 illustrates the static mapping networking. The router is an access gateway on the ISP network.

Figure 1 NAT Server and source NAT networking

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.
NAT Server		Name: policy_web Public IP address: 1.1.1.10 Private IP address: 10.2.0.7 Public port: 8080 Private port: 80	When Internet users send traffic to 1.1.1.10 through port 8080, the FW can forward the traffic to the web server based on this mapping entry. On the web server, the private address is 10.2.0.7, and the private port number is 80.
NAT Server		Name: policy_ftp Public IP address: 1.1.1.10 Private IP address: 10.2.0.8 Public port: 21 Private port: 21	When Internet users send traffic to 1.1.1.10 through port 21, the FW can forward the traffic to the FTP server based on this mapping entry. On the FTP server, the private address is 10.2.0.8, and the private port number is 21.
NAT address pool		10.2.0.10-10.2.0.15	-
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 NAT Server. Configure two server mapping entries, one for the web server and the other for the FTP server.
Configure a source NAT policy to translate the source addresses of packets accessing intranet servers into addresses in the NAT address pool.
Configure a default route on the FW to direct intranet traffic to the ISP 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 NAT address pool and enable port translation.

[FW] nat address-group addressgroup1
[FW-address-group-addressgroup1] mode pat
[FW-address-group-addressgroup1] section 0 10.2.0.10 10.2.0.15
[FW-address-group-addressgroup1] route enable
[FW-address-group-addressgroup1] quit

Configure a source 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-zone dmz
[FW-policy-nat-rule-policy_nat1] destination-address range 10.2.0.7 10.2.0.8
[FW-policy-nat-rule-policy_nat1] service http
[FW-policy-nat-rule-policy_nat1] service ftp
[FW-policy-nat-rule-policy_nat1] action source-nat address-group addressgroup1
[FW-policy-nat-rule-policy_nat1] quit
[FW-policy-nat] quit

Configure NAT Server. Configure two server mapping entries, one for the web server and the other for the FTP server.

[FW] nat server policy_web protocol tcp global 1.1.1.10 8080 inside 10.2.0.7 www unr-route

[FW] nat server policy_ftp protocol tcp global 1.1.1.10 ftp inside 10.2.0.8 ftp unr-route

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
```
Configure a blackhole route to prevent routing loops between the FW and router.
```
[FW] ip route-static 1.1.1.10 32 NULL 0
```
On the router, configure a static route, in which the destination address is 1.1.1.10 and the next-hop address is 1.1.1.1. The router directs traffic destined for 1.1.1.10 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
#
 nat server policy_web protocol tcp global 1.1.1.10 8080 inside 10.2.0.7 www unr-route

 nat server policy_ftp protocol tcp global 1.1.1.10 ftp inside 10.2.0.8 ftp unr-route

#
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 1.1.1.10 255.255.255.255 NULL0 
# 
nat address-group addressgroup1 0
 mode pat
 route enable
 section 0 10.2.0.10 10.2.0.15 
#  
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-zone dmz  
    destination-address range 10.2.0.7 10.2.0.8   
    service http
    service ftp
    action source-nat address-group addressgroup1  
# 
return