Description of problem:
The net/ipv6/.*/{accept_dad,optimistic_dad} should be able to be set for
all interfaces by setting
/proc/sys/net/ipv6/default/{accept_dad,optimistic_dad}

This does not work currently (confirmed with Hannes) and the only way to set 
these values is to do it for each interface.

So doing the following won't work:
[root@haa-08 ipv6]# cat /etc/sysctl.d/90-ipv6-disable-dad.conf
net.ipv6.conf.default.optimistic_dad=1                        

The only way to do it is to do it per interface:
net.ipv6.conf.eth0.optimistic_dad=1

The problem with this approach is that you can't really set up a new system
where DAD is fully disabled (or optimistic DAD enabled). You need to know and
set each interface explicitly, which is particularly hard given that we
have predictable naming for interfaces these days.


Version-Release number of selected component (if applicable):
3.10.0-327.13.1.el7.x86_64


Additional info:
This BZ was filed after a discussion in BZ#1245951