subnet calculator

subnetter.sh

if [ $# -ne 2 ]; then
  echo "Please provide CIDR and number of subnets"
  exit
fi

rx='^([0-9]{1,3}\.){3}[0-9]{1,3}(\/([0-9]|[1-2][0-9]|3[0-2]))?$';
if ! [[ $1 =~ $rx ]];then
 echo "Invalid CIDR";
 exit
fi

if ! [[ "$2" =~ ^[0-9]+$ ]];then
    echo "Integer is expected for subnets"
    exit
fi

SUBNET=$1;
NETWORK=`echo $SUBNET | cut -d / -f1`
MASK_BITS=`echo $SUBNET | cut -d / -f 2`;

if ! [[ "$MASK_BITS" =~ ^[0-9]+$ ]];then
    echo "Invalid CIDR, please append mask bits eg. 11.0.0.0/24"
    exit
fi

if [ $MASK_BITS -gt 31 ]; then 
  echo "Invalid mask bits, it should be less than 32"
  exit
fi

REQUIRED_SUBNETS=$2;
MAX_SUBNETS=$((32-MASK_BITS));
TOTAL_HOSTS=$((2**MAX_SUBNETS));

if [ $TOTAL_HOSTS -lt 12 ]; then
  echo "Required subnets should be at least 12"
  exit
fi 

if [ $REQUIRED_SUBNETS -gt $TOTAL_HOSTS ]; then
  echo "Required subnets should be less than the available hosts"
  exit
fi  

round() {
  printf "%.${2}f" "${1}"
}

get_subnets(){
     HOSTS_ARRAY=();
     HOSTS_ARRAY+=("$((TOTAL_HOSTS))");
     COUNT=${#HOSTS_ARRAY[@]};
     
     
      while [ $COUNT -le $REQUIRED_SUBNETS ]
      do
          temp=${HOSTS_ARRAY[0]}; 
          HOSTS_ARRAY=("${HOSTS_ARRAY[@]:1}")  
          HOSTS_ARRAY+=("$((temp/2))");
          HOSTS_ARRAY+=("$((temp/2))");  
          COUNT=$((${#HOSTS_ARRAY[@]}+1));
      done
     

     for hosts in "${HOSTS_ARRAY[@]}"
      do
        AVL_HOSTS=$((hosts-3));

        #SUBNET
        SUBNET_MASK_BITS=$(round $(echo "scale=10; l($hosts)/l(2)" | bc -l) 0);
        SUBNET_MASK_BITS=$((32-SUBNET_MASK_BITS));
        SUBNET=$NETWORK/$SUBNET_MASK_BITS;

        #BROADCAST
        BROADCAST_LAST_OCTET=`echo $NETWORK | cut -d . -f 4`
        BROADCAST=`echo $NETWORK | cut -d"." -f1-3`;
        BROADCAST="$BROADCAST.$(($BROADCAST_LAST_OCTET+$hosts-1))";

        #GATEWAY
        NETWORK_LAST_OCTET=`echo $NETWORK | cut -d . -f 4`
        GATEWAY=`echo $NETWORK | cut -d"." -f1-3`;
        GATEWAY="$GATEWAY.$((NETWORK_LAST_OCTET+1))";

        #display 
        echo "subnet="$SUBNET "network="$NETWORK "broadcast="$BROADCAST "gateway="$GATEWAY "hosts="$AVL_HOSTS;
        
        #NETWORK
        NETWORK_LAST_OCTET=`echo $NETWORK | cut -d . -f 4`
        NETWORK=`echo $NETWORK | cut -d"." -f1-3`;
        NETWORK="$NETWORK.$(($NETWORK_LAST_OCTET+$hosts))";

      done
}

get_subnets;