Web: Example for Configuring NAPT for Intranet Users to Access the Internet (Limiting the Number of Private Addresses Corresponding to a Public Address)

This section provides an example for configuring NAPT for intranet users to access the Internet.

Networking Requirements

An enterprise has deployed a FW as a security gateway on the intranet border. A source NAT policy needs to be configured on the FW so that users on the intranet 10.1.1.0/24 can access the Internet. In addition to the public IP address of the WAN interface on the FW, the enterprise has also been allocated public addresses 1.1.1.10 through 1.1.1.15 by the Internet service provider (ISP). The FW uses source NAT to map private addresses of the intranet (10.1.1.0/24) to these public addresses. If there are many intranet users access the Internet, port conflicts may occur during NAT. To reduce the possibility of port conflicts, you can set the maximum number of private addresses corresponding to a public address. Figure 1 illustrates the source NAT policy networking. The router is an access gateway on the ISP network.

Figure 1 Source NAT policy networking

Data Planning

Item		Data	Description
GigabitEthernet 0/0/1		IP address: 10.1.1.1/24 Security zone: trust	Set the default gateway address on each intranet host to 10.1.1.1.
GigabitEthernet 0/0/2		IP address: 1.1.1.1/24 Security zone: untrust	1.1.1.1/24 is a public address provided by the ISP.
Intranet segment that is allowed to access the Internet		10.1.1.0/24	-
Public addresses mapped to private addresses		1.1.1.10 to 1.1.1.15	As private addresses far outnumber public addresses, one-to-one mapping cannot be implemented. To translate all private addresses into public addresses, enable port translation.
Maximum number of private addresses corresponding to a public address		256	-
Routing information	FW's default route	Destination address: 0.0.0.0 Next hop address: 1.1.1.254	Configure a default route on the FW to direct intranet traffic to the ISP network.
Routing information	Router's static route	Destination address: 1.1.1.10 to 1.1.1.15 Next hop address: 1.1.1.1	The public addresses mapped to private addresses are not assigned to physical ports. As a result, the router cannot use a routing protocol to discover routes to the public addresses. Ask the ISP network administrator to configure a static route destined for the network segment address of the address pool on 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 to allow a specific intranet segment to access the Internet.
Configure a NAT address pool and enable port translation for public address multiplexing. Allow a maximum of 256 private addresses to be translated into one public address.
Configure a source NAT policy for translating source addresses between private and public address realms when hosts on the specific intranet segment access the Internet.
Configure a default route on the FW to direct intranet traffic to the ISP router.
Configure the IP address of the FW interface connected to the intranet as the default gateway address on each intranet host so that intranet traffic is directed to the FW when intranet hosts access the Internet.
Configure a static route on the ISP router for forwarding Internet traffic to the FW.

Procedure

Set IP addresses for interfaces on the FW and assign the interfaces to security zones.
1. Set the IP address of GigabitEthernet 0/0/1 and assign the interface to a security zone.
  1. Choose Network > Interface.
  2. In Interface List, click of GigabitEthernet 0/0/1 and set the parameters as follows:
    
    Zone
    
    trust
    
    IPv4
    
    IP Address
    
    10.1.1.1/24
  3. Click OK.
2. Set the IP address of GigabitEthernet 0/0/2 and assign the interface to a security zone.
  1. In Interface List, click of GigabitEthernet 0/0/2 and set the following parameters.
    
    Zone
    
    untrust
    
    IPv4
    
    IP Address
    
    1.1.1.1/24
  2. Click OK.
Configure a security policy to allow users on a specific network to access the Internet.
1. Choose Policy > Security Policy > Security Policy.
2. In Security Policy List, click Add, select Add Security Policy, and configure a security policy based on the following parameter values.
  
  Name
  
  policy1
  
  Source Zone
  
  trust
  
  Destination Zone
  
  untrust
  
  Source Address/Region
  
  10.1.1.0/24
  
  Action
  
  Permit
3. Click OK.
Configure a NAT address pool and a NAT policy.
1. Choose Policy > NAT Policy > NAT Policy > Source Translation Address Pool.
2. In Source Translation Address Pool List, click Add and configure a NAT address pool based on the following parameter values.
3. Click OK.
4. Choose Policy > NAT Policy > NAT Policy > NAT Policy.
5. In NAT Policy List, click Add and configure a NAT policy based on the following parameter values.
6. Click OK.
Configure a default route on the FW, so that traffic from the private network can be forwarded to the ISP router.
1. Choose Network > Route > Static Route.
2. In Static Route List, click Add and configure a default route based on the following parameter values.
  
  Protocol
  
  IPv4
  
  Destination Address/Mask
  
  0.0.0.0/0.0.0.0
  
  Next Hop
  
  1.1.1.254
3. Click OK.
On each PC, configure the IP address of the FW interface connected to the intranet as the default gateway address to direct intranet traffic to the FW. The detailed configuration process is omitted.
On the router, configure a static route destined for the network segment of the address pool (1.1.1.10 to 1.1.1.15) and set the next-hop address of the static route to 1.1.1.1 so that Internet traffic destined for the intranet server can be forwarded by the FW.
Contact your ISP administrator to perform this step.

Zone	trust
IPv4
IP Address	10.1.1.1/24

Zone	untrust
IPv4
IP Address	1.1.1.1/24

Name	policy1
Source Zone	trust
Destination Zone	untrust
Source Address/Region	10.1.1.0/24
Action	Permit

Protocol	IPv4
Destination Address/Mask	0.0.0.0/0.0.0.0
Next Hop	1.1.1.254

Configuration Scripts

Configuration script for the FW:

#
 sysname FW
#
interface GigabitEthernet0/0/1
 undo shutdown
 ip address 10.1.1.1 255.255.255.0 
#
interface GigabitEthernet0/0/2
 undo shutdown
 ip address 1.1.1.1 255.255.255.0 
#
firewall zone trust
 set priority 85
 add interface GigabitEthernet0/0/1
#
firewall zone untrust
 set priority 5
 add interface GigabitEthernet0/0/2
#
 ip route-static 0.0.0.0 0.0.0.0 1.1.1.254 
# 
nat address-group addressgroup1 0
 mode pat
 route enable
 section 0 1.1.1.10 1.1.1.15
 srcip-car-num 256 
#  
security-policy   
  rule name policy1  
    source-zone trust 
    destination-zone untrust 
    source-address 10.1.1.0 24  
    action permit 
#  
nat-policy  
  rule name policy_nat1 
    source-zone trust 
    destination-zone untrust  
    source-address 10.1.1.0 24   
    action source-nat address-group addressgroup1  
#                                          
return