Enables knotd+kresd to serve as a replacement for DNSmasq and still retain the dynamic DNS updates from DHCPv4 & DHCPv6 leases.

knot-odhcpd-dynamic-updates.sh

#!/bin/sh 

# Configuration 
lease_file='/tmp/hosts/odhcpd'
forward_zone='ber.section.me.'
reverse_zone_ipv4='1.168.192.in-addr.arpa.'
reverse_zone_ipv6='f.d.0.5.0.7.4.0.1.0.0.2.ip6.arpa.'

# Function for code reusability and readability
expand_ipv6() {
    ip=$1
    # Handle leading ::
    echo $ip | grep -qs "^:" && ip="0${ip}"
    # Expand ::
    if echo $ip | grep -qs "::"; then
        colons=$(echo $ip | sed 's/[^:]//g')
        missing=$(echo ":::::::::" | sed "s/$colons//")
        expanded=$(echo $missing | sed 's/:/:0/g')
        ip=$(echo $ip | sed "s/::/$expanded/")
    fi
    # Split into blocks
    blocks=$(echo $ip | grep -o "[0-9a-f]\\+")
    set $blocks
    printf "%04x:%04x:%04x:%04x:%04x:%04x:%04x:%04x\\n" \
        $(hex2dec $1) \
        $(hex2dec $2) \
        $(hex2dec $3) \
        $(hex2dec $4) \
        $(hex2dec $5) \
        $(hex2dec $6) \
        $(hex2dec $7) \
        $(hex2dec $8)
}

# Function to convert hex to dec (portable version)
hex2dec() {
    [ "$1" != "" ] && printf "%d" "$(( 0x$1 ))"
}

# Function to reverse a string
reverse_string() {
    input=$1
    reversed=""
    while [ -n "$input" ]; do
        # Extract the last character and append it to the reversed string
        last_char=$(echo "$input" | sed 's/.*\(.\)$/\1/')
        reversed="${reversed}${last_char}"
        # Remove the last character from the input string
        input=$(echo "$input" | sed 's/.\{1\}$//')
    done
    echo "$reversed"
}

# Function to convert an IPv6 address to reverse DNS format
ipv6_to_dns() {
    ip=$(expand_ipv6 $1)
    # Remove colons
    ip=$(echo $ip | tr -d ':')
    # Reverse the nibbles
    rev_ip=$(reverse_string $ip)
    # Insert dots between the nibbles
    rev_ip=$(echo $rev_ip | sed 's/./&./g')
    # Append .ip6.arpa
    echo "${rev_ip}ip6.arpa."
}

update_records() {
  hostname=$1
  ip=$2
  ip_type=$3 

  if [ "$ip_type" = "IPv4" ]; then
    set -- $(echo "$ip" | tr '.' ' ') 
    reverse_ip="$4.$3.$2.$1"
    last_octet="$4"
    ptr_record="$last_octet.$reverse_zone_ipv4"
  else  # IPv6
    ptr_record=$(ipv6_to_dns $ip)
  fi

  echo "Updating $hostname <-> $ip"

  # Update DNS records (forward and reverse zones)
  knotc zone-begin $forward_zone
  knotc zone-unset $forward_zone $hostname $([ "$ip_type" = "IPv4" ] && echo A || echo AAAA)
  knotc zone-set $forward_zone $hostname 300 $([ "$ip_type" = "IPv4" ] && echo A || echo AAAA) $ip
  knotc zone-commit $forward_zone

  knotc zone-begin $([ "$ip_type" = "IPv4" ] && echo $reverse_zone_ipv4 || echo $reverse_zone_ipv6)
  knotc zone-unset $([ "$ip_type" = "IPv4" ] && echo $reverse_zone_ipv4 || echo $reverse_zone_ipv6) $ptr_record PTR
  knotc zone-set $([ "$ip_type" = "IPv4" ] && echo $reverse_zone_ipv4 || echo $reverse_zone_ipv6) $ptr_record 300 PTR $hostname.$forward_zone
  knotc zone-commit $([ "$ip_type" = "IPv4" ] && echo $reverse_zone_ipv4 || echo $reverse_zone_ipv6)
}

# Lease parsing
while read -r line; do
  if [ "${line:0:1}" != "#" ]; then
    ip=$(echo $line | cut -d ' ' -f1)
    hostname=$(echo $line | cut -d ' ' -f2)

    # IP Validation with improved IPv6 check
    if echo "$ip" | grep -qE '^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$'; then
        ip_type="IPv4"
    elif echo "$ip" | grep -qE '(([0-9a-fA-F]{1,4}:){7}[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}:){1,7}:|([0-9a-fA-F]{1,4}:){1,6}:[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}:){1,5}(:[0-9a-fA-F]{1,4}){1,2}|([0-9a-fA-F]{1,4}:){1,4}(:[0-9a-fA-F]{1,4}){1,3}|([0-9a-fA-F]{1,4}:){1,3}(:[0-9a-fA-F]{1,4}){1,4}|([0-9a-fA-F]{1,4}:){1,2}(:[0-9a-fA-F]{1,4}){1,5}|[0-9a-fA-F]{1,4}:((:[0-9a-fA-F]{1,4}){1,6})|:((:[0-9a-fA-F]{1,4}){1,7}|:)|fe80:(:[0-9a-fA-F]{0,4}){0,4}%[0-9a-zA-Z]{1,}|::(ffff(:0{1,4}){0,1}:){0,1}((25[0-5]|(2[0-4]|1{0,2}[0-9]){0,1}[0-9])\.){3,3}(25[0-5]|(2[0-4]|1{0,2}[0-9]){0,1}[0-9])|([0-9a-fA-F]{1,4}:){1,4}:((25[0-5]|(2[0-4]|1{0,2}[0-9]){0,1}[0-9])\.){3,3}(25[0-5]|(2[0-4]|1{0,2}[0-9]){0,1}[0-9]))' ; then
        ip_type="IPv6"
    else
        echo "Invalid IP address: $ip" >&2
        continue
    fi

   update_records "$hostname" "$ip" "$ip_type"
  fi
done < "$lease_file"