Configuring Redirect NTP Responses on pfSense

Introduction

In this article, we will discuss how to configure redirect NTP responses in pfSense. NTP (Network Time Protocol) is a protocol used to synchronize the clock time between computers over a network. By default, pfSense does not respond to NTP requests. However, you can configure it to redirect NTP requests to a specific server.

Configuring Redirect NTP Responses Using iptables (First Approach)

The first approach to configuring NTP redirection in pfSense involves using iptables. iptables is a user-space utility program that allows you to configure the IP packet filter rules of the Linux kernel firewall, netfilter.

Step 1: SSH into pfSense

Connect to your pfSense firewall using SSH. The default username is "admin" and the default password is "pfsense".

Step 2: Enable SSH

If SSH is not already enabled, you will need to enable it. Go to the System > Advanced menu, and under the "Miscellaneous" section, check the "Enable SSH" box and save the changes.

Step 3: Install iptables

By default, pfSense does not come with iptables installed. To install it, use the following command:

# pkg install -y pf-tools

Step 4: Configure iptables

To configure iptables to redirect NTP requests, use the following command:

# iptables -t nat -A PREROUTING -p udp --dport 123 -j REDIRECT --to-ports 123:123

This command will redirect all incoming NTP requests on port 123 to port 123 on the local machine.

Step 5: Save the iptables rules

To save the iptables rules, use the following command:

# service pf save

Configuring Redirect NTP Responses Using pfSense (Recommended Approach)

The recommended approach to configuring NTP redirection in pfSense is to use the built-in NTP server and configure it to forward requests to an external NTP server.

Step 1: Configure the External NTP Server

First, you need to configure the external NTP server that you want to forward requests to. You can use any publicly available NTP server, or configure your own.

Step 2: Configure the pfSense NTP Server

Go to the Services > NTP menu, and under the "Servers" tab, add the IP address or hostname of the external NTP server. Make sure that the "Enable" checkbox is checked.

Step 3: Configure the pfSense Firewall

Go to the Firewall > Rules menu, and add a new rule. Set the source to be any, the destination to be the IP address or hostname of the external NTP server, and the protocol to be UDP. Make sure that the "Action" is set to "Pass".

First Approach: Use iptables to redirect NTP requests to a local machine running an NTP server.
Second Approach: Use the built-in NTP server in pfSense and configure it to forward requests to an external NTP server.