IPTables NAT Configuration: Laptop to OrangePi1 to OrangePi2

IPTables NAT Configuration: Laptop & Orange Pi 1 & Orange Pi 2

In this article, we will discuss how to configure IP Tables to set up a NAT (Network Address Translation) network involving a Laptop, Orange Pi 1, and Orange Pi 2. This configuration will allow the Orange Pi 2 to access the internet through the Laptop's network connection.

Prerequisites

Before we begin, make sure that you have the following:

• A Laptop with a network connection
• An Orange Pi 1 with a network connection
• An Orange Pi 2 with a network connection
• A basic understanding of IP Tables and NAT

Network Diagram

The following is a diagram of the network configuration:

+---------------+          +---------------+          +---------------+
|     Laptop    | <------> |   Orange Pi 1  | <------> |   Orange Pi 2  |
| (DHCP Address)|          | (DHCP Address)|          | (Static      |
+---------------+          +---------------+          | Address)      |
                                                        +---------------+

IPTables Configuration

To configure IP Tables for NAT, we need to perform the following steps:

1. Allow forwarding of packets between the interfaces
2. NAT the packets going from Orange Pi 2 to the internet
3. Log the NATed packets

Step 1: Allow forwarding of packets between the interfaces

By default, Linux distributions do not allow forwarding of packets between interfaces. To enable packet forwarding, we need to modify the sysctl configuration.

# echo 1 > /proc/sys/net/ipv4/ip_forward

To make this change persistent, we need to modify the sysctl configuration file:

# vi /etc/sysctl.conf

# Add the following line to the file
net.ipv4.ip_forward = 1

Step 2: NAT the packets going from Orange Pi 2 to the internet

To NAT the packets going from Orange Pi 2 to the internet, we need to add the following IP Tables rules:

# iptables -t nat -A POSTROUTING -o  -j MASQUERADE
# iptables -A FORWARD -i  -o  -m state --state RELATED,ESTABLISHED -j ACCEPT
# iptables -A FORWARD -i  -o  -j ACCEPT

Replace with the name of the interface connected to Orange Pi 2.

Step 3: Log the NATed packets

To log the NATed packets, we can add the following IP Tables rule:

# iptables -A FORWARD -m limit --limit 5/min -j LOG --log-prefix "IPTables-Dropped: " --log-level 7

In this article, we discussed how to configure IP Tables for NAT involving a Laptop, Orange Pi 1, and Orange Pi 2. We covered the prerequisites, network diagram, and IP Tables configuration steps. With this configuration, Orange Pi 2 can access the internet through the Laptop's network connection.

References

• systemd.network(5)
• Predicate Matching
• Network configuration