[FS#1002] Dns ipv6 problem when interface restart

[LEDE Bugs]

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FS#1002 - Dns ipv6 problem when interface restart
User who did this - Ansuel (Ansuel)

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2 problems...
Dual-stack (solved by adding a second pppoe... https://forum.lede-project.org/t/problem-with-ipv6-and-mobile-device/241/52)
Random dns disappear

When i put data here i use that exact config... 

In luci-->Network-->Interface i click connect 

My device connect to lan... with dual stack guest interface doesn't have any problem as it have only ipv4 address.

ubus list :
root at Ansuel-Router:~# ubus list network.interface.*
network.interface.guest
network.interface.lan
network.interface.loopback
network.interface.modem
network.interface.wan
network.interface.wan6

root at Ansuel-Router:~# ifstatus wan6
{
        "up": true,
        "pending": false,
        "available": true,
        "autostart": true,
        "dynamic": false,
        "uptime": 31,
        "l3_device": "pppoe-wan",
        "proto": "dhcpv6",
        "device": "pppoe-wan",
        "metric": 0,
        "dns_metric": 0,
        "delegation": true,
        "ipv4-address": [

        ],
        "ipv6-address": [
                {
                        "address": "2a01:2000:2000:463::1",
                        "mask": 64,
                        "preferred": 604788,
                        "valid": 2591988
                }
        ],
        "ipv6-prefix": [
                {
                        "address": "2a01:2000:2001:e5ea::",
                        "mask": 64,
                        "preferred": 319,
                        "valid": 319,
                        "class": "wan6",
                        "assigned": {
                                "guest": {
                                        "address": "2a01:2000:2001:e5ea::",
                                        "mask": 64
                                }
                        }
                }
        ],
        "ipv6-prefix-assignment": [

        ],
        "route": [
                {
                        "target": "2a01:2000:2000:463::",
                        "mask": 64,
                        "nexthop": "::",
                        "metric": 256,
                        "valid": 2591988,
                        "source": "::\/0"
                },
                {
                        "target": "::",
                        "mask": 0,
                        "nexthop": "fe80::90:1a00:1a4:d80f",
                        "metric": 512,
                        "valid": 28,
                        "source": "2a01:2000:2000:463::1\/64"
                },
                {
                        "target": "::",
                        "mask": 0,
                        "nexthop": "fe80::90:1a00:1a4:d80f",
                        "metric": 512,
                        "valid": 28,
                        "source": "2a01:2000:2001:e5ea::\/64"
                }
        ],
        "dns-server": [
                "2001:4b18:3050:916f::53:c001",
                "2001:4b18:3050:916f::53:c002"
        ],
        "dns-search": [

        ],
        "inactive": {
                "ipv4-address": [

                ],
                "ipv6-address": [

                ],
                "route": [

                ],
                "dns-server": [

                ],
                "dns-search": [

                ]
        },
        "data": {
                "passthru": "0017002020014b183050916f000000000053c00120014b183050916f000000000053c002"
        }
}

also what is this?
Sat Sep  9 19:24:51 2017 daemon.warn odhcpd[1389]: A default route is present but there is no public prefix on br-lan thus we don't announce a default route!

after about 160 sec   "ipv6-prefix"  reset to 360 (is it good? )

second try ok

found the problem... if i click (from the gui) connect to wan6 interface and then wan interface... wan6 gets ip but doesn't get dns
(and if I retry to ifdown/ifup wan6 it doesn't get dns)
(and also if i ifdown/ifup wan nothing change)

root at Ansuel-Router:~# ifstatus wan6
{
        "up": true,
        "pending": false,
        "available": true,
        "autostart": true,
        "dynamic": false,
        "uptime": 60,
        "l3_device": "pppoe-wan",
        "proto": "dhcpv6",
        "device": "pppoe-wan",
        "metric": 0,
        "dns_metric": 0,
        "delegation": true,
        "ipv4-address": [

        ],
        "ipv6-address": [
                {
                        "address": "2a01:2000:2000:466::1",
                        "mask": 64,
                        "preferred": 604770,
                        "valid": 2591970
                }
        ],
        "ipv6-prefix": [

        ],
        "ipv6-prefix-assignment": [

        ],
        "route": [
                {
                        "target": "2a01:2000:2000:466::",
                        "mask": 64,
                        "nexthop": "::",
                        "metric": 256,
                        "valid": 2591970,
                        "source": "::\/0"
                },
                {
                        "target": "::",
                        "mask": 0,
                        "nexthop": "fe80::90:1a00:1a4:d80f",
                        "metric": 512,
                        "valid": 10,
                        "source": "2a01:2000:2000:466::1\/64"
                }
        ],
        "dns-server": [

        ],
        "dns-search": [

        ],
        "inactive": {
                "ipv4-address": [

                ],
                "ipv6-address": [

                ],
                "route": [

                ],
                "dns-server": [

                ],
                "dns-search": [

                ]
        },
        "data": {

        }
}


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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=1002#comment3449