You need to update and configure following files for IPv6 configuration:
1. Edit: /etc/sysconfig/network
And append following line, to enable in systemwide the ipv6 protocol:
NETWORKING_IPV6=yes
2. Edit: /etc/sysconfig/network-scripts/ifcfg-eth1 (or your interface number)
And append following line, to enable ipv6 on interface and the address/gateway if you use static routing:
IPV6INIT=yes
IPV6ADDR=2001:1418:0193:000B::210
IPV6_DEFAULTGW=2001:1418:0193:000B::251
Save, close and restart network service:
# service network restart