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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

Just posted a patch upstream: https://marc.info/?m=150523120610624

Applied in davem/net:
https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/commit/?id=35e015e1f5773417952fe91ce8790baf9b4237a2

backporting it

Patch(es) committed on kernel repository and an interim kernel build is undergoing testing

Patch(es) available on kernel-3.10.0-764.el7

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2018:1062