Let’s break down what this script does in detail. The script is named dns_check.sh, authored by GJS (homelab-alpha), and its purpose of assessing network connectivity and the availability of DNS servers. While it doesn’t execute specific tasks, it’s instrumental in diagnosing potential network-related issues.

Here’s a detailed explanation:

Script Metadata

  • Filename: dns_check.sh
  • Author: GJS (homelab-alpha)
  • Date: 2024-05-26
  • Version: 1.0.1
  • Description: The script checks network connectivity and DNS server availability, aiding in troubleshooting network problems.
  • RAW Script: dns_check.sh

The script employs a function named dns-checker() to carry out the network checks. Let’s dissect its components:


ANSI Color Codes 

green="\e[32m"   # Green color code
red="\e[31m"     # Red color code
end="\e[0m"      # Reset text formatting

These variables store ANSI color codes for green, red, and resetting text formatting, enhancing the readability of log messages.


Timestamp 

stamp="$(date +'[%b %d, %Y - %H%M%S]')" # Timestamp for log messages

This line generates a timestamp to append to log messages, providing a chronological context for network events.


Logging Function 

function log_message() {
  local message="$1"
  echo -e "$stamp $message"
}

The log_message() function facilitates logging by adding timestamps to provided messages and echoing them to the console.


Ping Checking Function 

function check_ping() {
  local host="$1"
  if ping -c 1 "$host" >/dev/null; then
    return 0
  else
    return 1
  fi
}

This function, check_ping(), tests the reachability of a specified host via a single ping. It returns 0 if successful and 1 if unsuccessful.


DNS Server Checks

The script checks the availability of primary and secondary local (internal) DNS servers, such as PiHole or AdGuard Home, as well as overall internet connectivity.

First, it pings the primary local DNS server and logs its status. If the primary DNS server is unreachable, it pings the secondary local DNS server to check its availability.

Next, the script tests overall network connectivity by attempting to reach google.com. If google.com is unreachable, the script indicates a potential network issue.

If the network appears to be down, the script performs further diagnostics by pinging external DNS servers (9.9.9.9 and 149.112.112.112). This helps determine if the problem lies with DNS failures or broader network issues.


Network Interface Logging 

ifconfig >>"DNS_failure_interface_${stamp}.txt"

In case of network failures, the script appends network interface information to a timestamped log file, aiding in subsequent troubleshooting.


Conclusion

In essence, dns_check.sh provides a comprehensive network diagnostic tool, assessing DNS server availability and network connectivity, and logging relevant information for troubleshooting purposes.

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Last updated 01 Sep 2024, 10:22 CEST . history