...
NETWORKING_IPV6=yes

DEVICE=eth0
BOOTPROTO=static
...
IPV6INIT=yes
IPV6_AUTOCONF=no
IPV6ADDR="2001:41D0:2:xxxx::/64"
IPV6_DEFAULTGW="2001:41d0:2:xxff:ff:ff:ff:ff"

...
net.ipv6.conf.all.autoconf = 0
net.ipv6.conf.default.autoconf = 0
net.ipv6.conf.eth0.autoconf = 0
net.ipv6.conf.all.accept_ra = 0
net.ipv6.conf.default.accept_ra = 0
net.ipv6.conf.eth0.accept_ra = 0
net.ipv6.conf.all.accept_redirects=0
net.ipv6.conf.all.router_solicitations=1
net.ipv6.conf.default.proxy_ndp=1
net.ipv6.conf.all.proxy_ndp=1
net.ipv6.conf.default.forwarding=1
net.ipv6.conf.all.forwarding = 1

eth0      ...
          inet6 addr: 2001:41d0:2:xxxx::/64 Scope:Global
          inet6 addr: fe80::230:48ff:fefd:7a86/64 Scope:Link

traceroute to ipv6.google.com (2a00:1450:4007:80d::200e), 30 hops max, 80 byte packetsping ipv6.
 1  2001:41d0:2:xxxx::)  3005.167 ms !H  3005.118 ms !H  3005.089 ms !H

ping: unknown host ipv6.google.com

2001:41D0:2:xxff:ff:ff:ff:ff dev eth0
default via 2001:41D0:2:xxff:ff:ff:ff:ff

Shutting down interface eth0:                              [  OK  ]
Shutting down loopback interface:                          [  OK  ]
Bringing up loopback interface:                            [  OK  ]

IPV6INIT=yes
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_PEERDNS=yes
IPV6_PEERROUTES=yes
IPV6_FAILURE_FATAL=yes
IPV6ADDR_SECONDARIES="2001:41D0:2:xxxx::1/64"