Generate Unique IPv6 Local Network

gen-ipv6-network.sh

#!/bin/bash
# Generates a unique local IPv6 network
# Based on RFC4193 https://www.rfc-editor.org/rfc/rfc4193#section-3.2.2

QUIET=0
while getopts :hqs: flag
do
    case "${flag}" in
    q) # Only output network prefix
        QUIET=1
        ;;
    s) # Specify 4 hexadecmil digits for subnet
        SUBNET=${OPTARG}
        ;;
    h | *) # Display help
        echo "Generates a RFC4193 compliant unique IPv6 local network prefix"
        echo "-q Only output network prefix"
        echo "-s Specify 4 hexadecmil digits for subnet"
        echo "-h Display help"
        exit 0
        ;;
    esac
done

if [ ! -z $SUBNET ]; then
        if [ ${#SUBNET} -ne 4 ] || ! [[ $SUBNET =~ ^[0-9A-Fa-f]{1,}$ ]]; then
                echo "Subnet can only be 4 hexadecimal characters"
                exit 0
        fi
fi

# Concatenate the current timestamp and machine ID
# Use sha1sum to geneate a hash
# Save the last 14 characters as the network hash
HASH=$(echo -n "$(date +%s%N)""$(cat /etc/machine-id)" | sha1sum | awk '{print substr($0,27,14)}')

# Use the last 10 characters from the network hash to generate a network
PREFIX=$(echo $HASH | awk '{print "fd" substr($0,4,2) ":" substr($0,7,4) ":" substr($0,11,4)}')
GID=$(echo $PREFIX | awk '{print substr($0,3)}')

if [ -z $SUBNET ]; then
        # Not part of the RFC; use the first 4 characters from the hash for a random subnet
        # Any subnet can be used if needed; ie. 0000, 0001, 8A7C
        SUBNET=$(echo $HASH | awk '{print substr($0,0,4)}')
fi

if [ $QUIET -eq 1 ];then
        echo "$PREFIX":"$SUBNET"::/64
else
        echo Gloabl ID: "$GID" 
        echo Unique Prefix: "$PREFIX"::/64
        echo Subnet: "$PREFIX":"$SUBNET"::/64
fi