Configure IPv6 in Ubuntu

Below post explains steps involved in configuring IPv6 networking in an Ubuntu server
1. First backup current network configuration:
#cp /etc/network/interfaces /etc/network/interfaces.backup  
How to delete an ipv6 address :  #ifconfig eth0 inet6 del 2604:2881::8fe5:27e2/64
How to add an ipv6 address :  #ifconfig eth0 inet6 add 2604:2881::8fe5:27e2/64
2. Add an IPv6 route through gateway  
           #route -A inet6 add 2604:2880::8fe5:27e2/64 gw <gateway ip>

#ip -6 route add 2604:2880::8fe5:27e2/64 via <gateway ip> #/etc/init.d/networking restart
To see the new ipv6 address :
#ip -6 address show eth0
To see ipv6 route :
# ip -6 route show dev eth0
To Permanently add IPV6 to the server, follow the below steps:
Append the below lines in "/etc/network/interfaces" file.

#vi /etc/network/interfaces
iface eth0 inet6 static
pre-up modprobe ipv6
address 2604:2880::8fe5:27e2/64
netmask 64
gateway 2247:f0d0:2001:000a:f0d0:2001::1
dns-nameservers 2001:4860:4860::8888 2001:4860:4860::8844

If ipv6 nameserver IPs are not there in /etc/resolv.conf then add Google Public DNS IPv6 addresses

nameserver 2001:4860:4860::8888
nameserver 2001:4860:4860::8844

#route -A inet6 add 2604:2880::8fe5:27e2/64 gw 2247:f0d0:2001:000a:f0d0:2001::1
#/etc/init.d/networking restart
To test ipv6 connectivity :