How to Create a BASH Backup Script that Connects IP Addresses to MAC Addresses

Learn how to easily modify your BASH backup script to adapt to changing IP addresses based on known MAC addresses, ensuring a seamless backup process.
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How to Create a BASH Backup Script that Connects IP Addresses to MAC Addresses

Managing backups for multiple devices on a local area network (LAN) can be tricky—especially when some devices frequently change their IP addresses. This is particularly true for laptops that might connect via WiFi instead of being docked to an Ethernet connection. In this guide, we will explore how you can enhance your BASH backup script to dynamically detect true IP addresses based on known MAC addresses and ensure that your backups run smoothly regardless of connectivity status.

The Problem at Hand

You have a BASH backup script that utilizes rsync to back up data from a set of known static devices. However, you face challenges when some laptop users fail to connect to their docks, causing them to be assigned temporary DHCP addresses when they connect via WiFi. You currently have a static list of devices with their known IPs and MACs, but you need a way to dynamically associate these with the current IPs assigned to the laptops, keeping your original targets clean for when the laptops are properly docked.

The Solution Overview

To address this issue, we can leverage the results of a network scan (using nmap) to identify current devices and their MAC addresses. We will create a mapping of detected IP addresses to MAC addresses, and then update our backup script to check this mapping when performing backups.

Step 1: Scan the Network and Create a Mapping

First, we will perform a network scan to obtain the IP addresses and associated MAC addresses of devices currently on the LAN. We can achieve this using the following command:

[[See Video to Reveal this Text or Code Snippet]]

This command will generate a list of currently detected devices and their MAC addresses, which we will save to a file called found.devices.

Step 2: Prepare Your Bash Script

Refresh your existing backup script to read from the found.devices file and cross-reference with your known.targets file. Below is a snippet of code that accomplishes this:

[[See Video to Reveal this Text or Code Snippet]]

Code Explanation

Associative Array Creation: The script creates an associative array called found_mac2ip that maps MAC addresses to their corresponding IP addresses. It reads from the found.devices file and fills this array.

Backup Loop: Then, it loops through the known.targets file, checking if each MAC address exists in our mapping. If a match is found, it uses the new IP address; otherwise, it retains the original IP from known.targets.

Alternative Method: Directly Extract Information from nmap

If you prefer not to create a found.devices file, you can extract IP and MAC address information directly from the output of nmap:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By implementing these simple modifications to your BASH backup script, you can ensure that your backups continue to function effectively regardless of device connectivity. This approach also allows you to keep your known targets file clean and organized.

Feel free to reach out if you have further questions or need additional assistance tweaking your script. Happy scripting!

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