Connected devices cannot use IPv6

Before the recommended config changes:

root@router:~# ifstatus wan6
{
        "up": true,
        "pending": false,
        "available": true,
        "autostart": true,
        "dynamic": false,
        "uptime": 29672,
        "l3_device": "eth1",
        "proto": "dhcpv6",
        "device": "eth1",
        "metric": 0,
        "dns_metric": 0,
        "delegation": true,
        "ipv4-address": [

        ],
        "ipv6-address": [
                {
                        "address": "2600:1007:a012:78c7:ca7f:54ff:fe24:a56a",
                        "mask": 64,
                        "preferred": 20,
                        "valid": 30
                }
        ],
        "ipv6-prefix": [

        ],
        "ipv6-prefix-assignment": [

        ],
        "route": [
                {
                        "target": "2600:1007:a012:78c7::",
                        "mask": 64,
                        "nexthop": "::",
                        "metric": 256,
                        "valid": 30,
                        "source": "::/0"
                },
                {
                        "target": "::",
                        "mask": 0,
                        "nexthop": "fe80::12e8:a7ff:fef3:aa01",
                        "metric": 512,
                        "valid": 35,
                        "source": "2600:1007:a012:78c7:ca7f:54ff:fe24:a56a/64"
                }
        ],
        "dns-server": [

        ],
        "dns-search": [

        ],
        "neighbors": [

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

                ],
                "ipv6-address": [

                ],
                "route": [

                ],
                "dns-server": [
                        "2001:4888:35:ff00:383:d::",
                        "2001:4888:34:ff00:386:d::"
                ],
                "dns-search": [

                ],
                "neighbors": [

                ]
        },
        "data": {

        }
}

After the recommended config changes:

root@router:~# ifstatus wan6
{
        "up": true,
        "pending": false,
        "available": true,
        "autostart": true,
        "dynamic": false,
        "uptime": 46,
        "l3_device": "eth1",
        "proto": "dhcpv6",
        "device": "eth1",
        "updated": [
                "prefixes"
        ],
        "metric": 0,
        "dns_metric": 0,
        "delegation": true,
        "ipv4-address": [

        ],
        "ipv6-address": [
                {
                        "address": "2600:1007:a012:78c7:ca7f:54ff:fe24:a56a",
                        "mask": 64,
                        "preferred": 26,
                        "valid": 36
                }
        ],
        "ipv6-prefix": [
                {
                        "address": "2600:1007:a012:78c7::",
                        "mask": 64,
                        "preferred": 26,
                        "valid": 36,
                        "class": "wan6",
                        "assigned": {
                                "lan": {
                                        "address": "2600:1007:a012:78c7::",
                                        "mask": 64
                                }
                        }
                }
        ],
        "ipv6-prefix-assignment": [

        ],
        "route": [
                {
                        "target": "::",
                        "mask": 0,
                        "nexthop": "fe80::12e8:a7ff:fef3:aa01",
                        "metric": 512,
                        "valid": 41,
                        "source": "2600:1007:a012:78c7:ca7f:54ff:fe24:a56a/64"
                }
        ],
        "dns-server": [

        ],
        "dns-search": [

        ],
        "neighbors": [

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

                ],
                "ipv6-address": [

                ],
                "route": [

                ],
                "dns-server": [
                        "2001:4888:35:ff00:383:d::",
                        "2001:4888:34:ff00:386:d::"
                ],
                "dns-search": [

                ],
                "neighbors": [

                ]
        },
        "data": {

        }
}

On connected devices, running ping -6 ``example.com no longer ends up in a “Network unreachable” error, but instead results in all IPv6 connections seemingly never finishing.

opnent@box ~ [2]> ping -6 example.com
PING example.com (2600:1406:5e00:6::17ce:bc12) 56 data bytes
^C
--- example.com ping statistics ---
55 packets transmitted, 0 received, 100% packet loss, time 55338ms

IPv6 still works as expected on the router itself.