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CentOS 7 & DHCPv6

Sometimes instead of the usual SLAAC you might need or want to use DHCPv6. The dhcp package and a very short manual configuration will take care of everything for you on the server, but what about the client? What if you configured the DHCPv6 client but it is not working?

I setup both the server and the firewall, then I proceeded to configure the client, but it would always fail. No v6 traffic would hit the server machine, even though I added the DHCPV6C=yes on the client machine. After hours spent without a solution, I found a video with the answer: the problem is Network Manager! On top of adding the DHCPV6C parameter you also need to add NM_CONTROLLED=no. I ended up with the following /etc/sysconfig/network-scripts/ifcfg-ethX:

TYPE=Ethernet
PROXY_METHOD=none
BROWSER_ONLY=no
BOOTPROTO=none
DEFROUTE=no
IPV4_FAILURE_FATAL=no
IPV4INIT=no
IPV6INIT=yes
NM_CONTROLLED=no
DHCPV6C=yes
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=no
IPV6_FAILURE_FATAL=no
IPV6_ADDR_GEN_MODE=stable-privacy
NAME=ethX
DEVICE=ethX
ONBOOT=yes
IPV6_PRIVACY=yes
ZONE=public

Perfectly disabled IPv4, IPv6 configured automatically, all fine and dandy. Happy fun times!