How to configure a highly available NAT gateway on Linux

How to configure a highly available NAT gateway on Linux

Summary:
Network address translation (NAT) is a common networking technology used to translate the IP address of a private network to a public network IP address. On Linux systems, configuring a highly available NAT gateway can improve network availability and reliability. This article will introduce how to use Keepalived and iptables tools to configure a highly available NAT gateway on Linux.

Keywords: NAT, high availability, Keepalived, iptables

Introduction:
In the modern network environment, network availability and reliability are very important. In order to achieve this goal, it is critical to configure a highly available NAT gateway. Highly available NAT gateways can work in active-standby mode to ensure that when a host fails, the standby gateway can automatically take over and keep the network running.

Step 1: Install and configure Keepalived
1.1 Install the Keepalived package:
Run the following command in the terminal to install the Keepalived package:

sudo apt-get install keepalived

1.2 Configure Keepalived:
Enter the configuration file directory of Keepalived and create a configuration file named keepalived.conf. Use the following sample configuration and modify it according to the actual situation:

global_defs {
router_id NatRouter
}

vrrp_script check_nat_gateway {
script "pidof keepalived"
interval 2
weight -1
}

vrrp_instance NatGateway {
state MASTER
interface eth0
virtual_router_id 1
priority 100
advert_int 1
authentication {

  auth_type PASS
  auth_pass YourPasswordHere

}
virtual_ipaddress {

  192.168.1.1/24

}
track_script {

  check_nat_gateway

}
}

Save and exit the configuration file.

Step 2: Configure iptables
In order to achieve a highly available NAT gateway, we also need to configure iptables so that it can correctly forward and process network traffic.

2.1 Enable IP forwarding:
Open the /etc/sysctl.conf file and find the following line:

net.ipv4.ip_forward=1

Uncomment this line so that it becomes:

net.ipv4.ip_forward=1

Save and exit the file. Then, run the following command in the terminal to make the modification effective:

sudo sysctl -p

2.2 Configure iptables:
Run the following command in the terminal to configure iptables:

sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

Save the iptables rules and write them to the persistence rules file so that they take effect when the system is restarted:

sudo iptables-save | sudo tee /etc/iptables/rules.v4

Step 3: Start and test the highly available NAT gateway
3.1 Start the Keepalived service:
Run the following command in the terminal to start Keepalived Service:

sudo service keepalived start

3.2 Test high availability:
Test the highly available NAT gateway through the ping command. Ping the virtual IP address (192.168.1.1) from another computer and if the network is OK, the backup gateway has taken over correctly.

Conclusion:
By using Keepalived and iptables, we can configure a highly available NAT gateway on a Linux system. This configuration ensures that when the primary gateway fails, the backup gateway can automatically take over, thereby improving network availability and reliability.

Reference:

• "How To Set Up a High Availability Rolling Update NAT Gateway with Keepalived and HAproxy on Ubuntu 14.04 | DigitalOcean" (https://www.digitalocean.com /community/tutorials/how-to-set-up-a-high-availability-rolling-update-nat-gateway-with-keepalived-and-haproxy-on-ubuntu-14-04)

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