Add remove multiple ipv6 addresses on prefix change

A bash script to add and delete multiple IPv6 addresses on prefix change.

First step is to create a text file with "0000:0000:0000:0000" as text which will store the IPv6 prefix of your server. Create a file using this example.

IPv6Prefix.txt

echo "0000:0000:0000:0000" > $HOME/IPv6Prefix.txt
chmod 777 $HOME/IPv6Prefix.txt

If you choose to manually create the file then first create a blank file IPv6Prefix.txt and save it in /root/IPv6Prefix.txt, now open the file and type 0000:0000:0000:0000 and save and close the file. For some reason the IPv6Prefix.txt should not be empty for comparison this is why I had to type zero and save the file. Give the permissions 0777 to IPv6Prefix.txt so the script can write to it.

Now the second step is to create a text file containing all your IPv6 suffixes that you want to add to your server. For example

ipv6-addresses.txt

printf %s '5e37:080b:66b7:68bb
52bf:52fe:a1df:60e3
3b32:a9d4:a9f3:074f
9ec7:f4da:b166:0a5f
620c:eb97:3e93:ece3
551b:dda7:d78d:c09a
cf34:cb8b:b1be:12a4
3600:af53:10ad:f647
9527:dcc4:4926:51ba
76a2:410f:704b:8d9c' >> $HOME/ipv6-addresses.txt

Now create a bash file to do all the processing. You need to create a schedule to periodically check the IPv6 prefix for change. Change the interface name (ens18) to the name of your interface.

ipv6-add-delete.sh

#!/bin/bash

IPv6PrefixFile=$HOME/IPv6Prefix.txt
IPv6Prefix=$(cat $IPv6PrefixFile)

__rfc5952_expand () {
read addr mask < <(IFS=/; echo $1)
quads=$(grep -oE "[a-fA-F0-9]{1,4}" <<< ${addr/\/*} | wc -l)
grep -qs ":$" <<< $addr && { addr="${addr}0000"; (( quads++ )); }
grep -qs "^:" <<< $addr && { addr="0000${addr}"; (( quads++ )); }
[ $quads -lt 8 ] && addr=${addr/::/:$(for (( i=1; i<=$(( 8 - quads )) ; i++ )); do printf "0000:"; done)}
addr=$(for quad in $(IFS=:; echo ${addr}); do printf "${delim}%04x" "0x${quad}"; delim=":"; done)
[ ! -z $mask ] && echo $addr/$mask || echo $addr
}

IPv6Current=$(/sbin/ip -6 addr | grep inet6 | grep -vE 'host|temporary' | grep -F 'scope global dynamic' | sed -e 's/^.*inet6 \([^ ]*\)\/.*$/\1/;t;d' | grep '^2' | head -n1)
IPv6Current="$(__rfc5952_expand $IPv6Current)"

IPv6Current=${IPv6Current:0:19}

if [ $IPv6Current != $IPv6Prefix ]; then

for i in $(cat $HOME/ipv6-addresses.txt);
do
	ip -6 addr del ${IPv6Prefix}:${i} dev ens18
	ip -6 addr add ${IPv6Current}:${i} dev ens18
done

echo $IPv6Current > $IPv6PrefixFile
fi

exit 0

The final step is to reset the file IPv6Prefix.txt on your computer startup or reboot. Create a crontab entry to reset the file on each reboot.

crontab -e

@reboot sleep 60 && echo "0000:0000:0000:0000" > $HOME/IPv6Prefix.txt

Let me know if you have any comments or if there is any error in this guide.

## Disclaimer

The software provided in this repository is for educational and informational purposes only. Under no circumstances shall the author or contributors be liable for any direct, indirect, incidental, special, exemplary, or consequential damages arising out of the use or inability to use this software. The author will not be liable for any special, incidental, consequential or indirect damages due to loss of data or any other reason.

Add remove multiple IPv6 addresses on prefix change