Description of problem:

Network validation during overcloud deployment fails with multiple ping errors like this:

01:20:22.347 stdout: {
01:20:22.347   "status": "FAILED", 
01:20:22.347   "server_id": "c64e0c01-9db8-460b-89ff-e63d9eb33e92", 
01:20:22.347   "config_id": "e24758a4-c991-44c6-9ddb-19c4caca6d2c", 
01:20:22.347   "output_values": {
01:20:22.347     "deploy_stdout": "Trying to ping fd00:fd00:fd00:2000:f816:3eff:fec5:4ca4 for local network fd00:fd00:fd00:2000::/64...FAILURE
01:20:22.347 ", 
01:20:22.347     "deploy_stderr": "fd00:fd00:fd00:2000:f816:3eff:fec5:4ca4 is not pingable. Local Network: fd00:fd00:fd00:2000::/64
01:20:22.347 ", 
01:20:22.347     "deploy_status_code": 1
01:20:22.347   }, 
01:20:22.347   "creation_time": "2016-01-17T16:51:40Z", 
01:20:22.347   "updated_time": "2016-01-17T16:52:17Z", 
01:20:22.347   "input_values": {}, 
01:20:22.347   "action": "CREATE", 
01:20:22.347   "status_reason": "deploy_status_code : Deployment exited with non-zero status code: 1", 
01:20:22.347   "id": "95cd202b-62f7-42fd-aecf-e52284cb08bf"
01:20:22.347 }

Version-Release number of selected component (if applicable):
7-director poodle 2016-01-17.1

How reproducible:
100%

Steps to Reproduce:
1. Deploy using IPv6

Actual results:

Failed ping tests. Note that logging into the overcloud, you can actually ping these addresses using ping6.

Expected results:

Passing ping tests.

Additional info:

We have a few theories for why this happens. Either we use the wrong ping (ping vs. ping6), or it could be that the validation runs very close to the time the addresses are added, so that they are in "tentative" state, not gotten through the Duplicate Address Detection (DAD).

If the problem is the latter, we might circumvent it by waiting a bit before the check, or disable DAD altogether on the interfaces with this command (probably):

sysctl -w net.ipv6.conf.all.accept_dad=0

http://www.tldp.org/HOWTO/Linux+IPv6-HOWTO/proc-sys-net-ipv6..html