NAT flow logging configuration examples

 

·     Introduction

·     Prerequisites

·     Example: Configuring NAT flow logging

 

The following information provides NAT flow logging configuration examples.

 

This document is not restricted to specific software or hardware versions. Procedures and information in the examples might be slightly different depending on the software or hardware version of the device.

The configuration examples were created and verified in a lab environment, and all the devices were started with the factory default configuration. When you are working on a live network, make sure you understand the potential impact of every command on your network.

The following information is provided based on the assumption that you have basic knowledge of flow logging, NAT logging, and NAT.

Network configuration

As shown in Figure 1, configure NAT flow logging on the device to enable it to send NAT session information to the log server for user tracing and analysis. The following log information is recorded when the internal host accesses the server on the public network: Source IP address, source port number, destination IP address, and destination port number before and after NAT translation.

Figure 1 Network diagram

 

Software versions used

This configuration example was created and verified on E8371 of the F5000-AI160 device and E9671 of the M9000-X06 device.

Restrictions and guidelines

·     To record IP address and port number after translation, use log version 3.0.

·     For the NAT flow logging to take effect, you must enable NAT logging.

·     Logs cannot be sent to the log host and the information center at the same time. By default, logs are sent to the log host. If the information center is specified as the log output destination, logs will not be sent to the log host.

Procedure

Configuring the device

1.     Assign IP addresses to interfaces and add the interfaces to security zones.

# On the top navigation bar, click Network.

# From the navigation pane, select Interface Configuration > Interfaces.

# Click the Edit icon for GE 1/0/0.

# In the dialog box that opens, configure the interface:

a.     Select the DMZ security zone.

b.     On the IPv4 Address tab, enter the IP address and mask of the interface. In this example, enter 192.168.100.200/24.

c.     Click OK.

# Add GE 1/0/1 to the Trust security zone and set its IP address to 172.16.1.254/24 in the same way you configure GE 1/0/0.

 

# Add GE 1/0/2 to the Untrust security zone and set its IP address to 202.2.2.1/24 in the same way you configure GE 1/0/0.

2.     Create security policy SecPolicy1.

# On the top navigation bar, click Policies.

# From the navigation pane, select Security Policies > Security Policies.

# Click Create and click Create a policy.

# In the dialog box that opens, configure a security policy:

¡     Enter policy name SecPolicy1.

¡     Select source zone Trust.

¡     Select destination zone Untrust.

¡     Select IPv4 as the type.

¡     Select action Permit.

¡     Specify 172.16.1.0/24 as the source address.

¡     Specify 202.2.2.0/24 as the destination address.

# Click OK.

3.     Create security policy SecPolicy2.

# On the top navigation bar, click Policies.

# From the navigation pane, select Security Policies > Security Policies.

# Click Create.

# In the dialog box that opens, configure a security policy:

¡     Enter policy name SecPolicy2.

¡     Select source zone Local.

¡     Select IPv4 as the type.

¡     Select destination zone DMZ.

¡     Select action Permit.

¡     Specify 192.168.100.0/24 as the destination address.

# Click OK.

4.     Configure a policy-based NAT rule.

# On the top navigation bar, click Policies.

# From the navigation pane, select Policy-based NAT.

# Click Create.

# Create a policy-based NAT rule, as shown in Figure 2.

Figure 2 Creating a policy-based NAT rule

 

# Click OK.

5.     Configure flow logging.

# On the top navigation bar, click System.

# From the navigation pane, select Log Settings > Basic Settings.

# On the Flow Log tab, configure flow logging, as shown in Figure 3.

Figure 3 Configure flow logging

 

6.     Configure NAT logging.

# On the top navigation bar, click System.

# From the navigation pane, select Log Settings > NAT Log Settings.

# Configure NAT logging, as shown in Figure 4.

Figure 4 Configure NAT logging

 

# Click Apply.

Configuring the log server

# Configure the log server. (Details not shown.)

Verifying the configuration

Verify that a NAT session log is generated on the log server when the host accesses the server on the public network. The log information includes source IP address, source port number, destination IP address, and destination port number before and after translation.