• Lucas
• April 06, 2024

Proxy ARP is a technique used to allow one machine to respond to ARP (Address Resolution Protocol) requests on behalf of another machine. This is useful in various situations, such as when you need to interconnect two subnets without routers or when you want to implement a high availability solution. In Linux, you can configure Proxy ARP by editing configuration files and using specific commands. Here’s a basic tutorial on how to do it:

Step 1: Check that the ARP Proxy is enabled on your system

1. Open a terminal.
2. Use the command cat /proc/sys/net/ipv4/conf/all/proxy_arp to check that the ARP Proxy is enabled. A value of 1 indicates that it is enabled, while 0 indicates that it is disabled.

Step 2: Enable Proxy ARP

If the ARP Proxy is not enabled, you can enable it as follows:

1. Temporarily (until the next restart):
   • Use the command echo 1 > /proc/sys/net/ipv4/conf/all/proxy_arp to enable the ARP Proxy temporarily.
2. Permanently:
   • Edit the file /etc/sysctl.conf and add the line net.ipv4.conf.all.proxy_arp = 1.
   • To apply the change without restarting, run sysctl -p.

Step 3: Configure Network Interfaces

For the ARP Proxy to work properly, you need to configure the network interfaces involved. This usually involves configuring IP addresses and ensuring that subnets are correctly set up.

1. Use the command ip addr add [endereço IP]/[máscara de rede] dev [nome da interface] to add an IP address to the desired interface.
2. Check the configuration with ip addr show.

Step 4: Test the configuration

To test whether the ARP Proxy is working as expected, you can use the arping command on another machine on the same network to check whether the machine with ARP Proxy enabled responds to ARP requests destined for a machine with a different IP address.

• Use arping -I [interface] [endereço IP da máquina alvo] to test.

Final considerations

• Remember that the use of the ARP Proxy can have implications for the security of your network, as it can be used to carry out man-in-the-middle attacks if it is not properly secured.
• It is important to fully understand the implications of enabling the ARP Proxy on your network and to configure it properly to avoid security problems.

This tutorial provides a basic overview of how to configure the ARP Proxy in Linux. Depending on your environment and specific needs, you may need to make additional settings or adjust the above steps.