CentOS

/etc/sysconfig/network

NETWORKING_IPV6=yes   

/etc/sysconfig/network-scripts/ifcfg-eth0

IPV6INIT=yes
IPV6ADDR=2A00:1128:1:1::xxx:xxx/64
IPV6_DEFAULTGW="fe80::1%eth0"

Debian

/etc/network/interfaces

iface eth0 inet6 static
address 2A00:1128:1:1::xxx:xxx
netmask 64
gateway fe80::1