IPv6 issues with D-Link 1510 series managed switch

[NSNE]

I recently bought a D-Link DGS-1510-28X managed switch in order to start my foray into 10G home networking.

The GUI is like something out of the late '90s, but I've been able to configure almost everything the way I want it.

I say "almost everything" because there's a persistent IPv6 issue. The switch doesn't seem to be able to connect to external IPv6 addresses—NTP servers in particular. It connects to IPv4 IP addresses just fine. However, pinging or tracerouting known IPv6 addresses results in an endless series of timeouts.

Any idea what the issue could be? Does anyone have IPv6 working successfully with this or another D-Link switch?

Some background:

• My ISP, modem and router are all fully IPv6 capable and configured properly. I get a score of 17/20 on https://ipv6-test.com, and the 17 is only because I won't authorize its certificates.
• All the other IPv6-capable devices on my LAN—including those connected to the switch—have IPv6 addresses and IPv6 connectivity.
• The switch appears to have a link-local IPv6 address and an IPv6 global unicast address.
  
• After no success with defaults, I tried entering Cloudflare's and Comcast's IPv6 DNS servers into the switch's DNS fields. Still didn't work.
• There's nothing fancy like VLANs or anything. I configured LAG (LACP) on four ports and that's about it.

 

[System Error Message]

for a lot less you could've gotten mikrotik or ubiquiti and even more features for 10G ethernet or SFP+

Dlink should be avoided always. When their dumb switches needed reboots, definitely doing something wrong. I could say the same about netgear though when their nice modem requires a reboot every 3 months, not quite the hardware quality known.

 

[NSNE]

for a lot less you could've gotten mikrotik or ubiquiti and even more features for 10G ethernet or SFP+.

This is a massive help. Can't thank you enough. I used a spare TARDIS I had lying around and traveled back to December. I no longer have this issue in that alternate timeline.

 

[NSNE]

I'll answer my own question on this in the hope that it'll help someone else.

Unlike previous forum suggestions, D-Link tech support was genuinely helpful and was able to point me in the right direction.

The solution involved setting a static/default IPv6 route. Even when devices are shown as "Directly connected" in IPv6 routes, it seems IPv6 needs (useful info here, here, here and especially here) more detailed routing info than IPv4. Packets apparently like to know where they're headed along every step of the network chain.

So I ending up specifying two routes. One was a default route of ::/0 with a next hop of FE80::. The second entry used my router's LAN delegated prefix as the first value and then FE80:: as the next hop again.

I'm not entirely sure if both entries are necessary, but IPv6 pings started being successful once both of them were there, so I left them. I can now ping internal and external IPv6 addresses on the switch, and it's communicating with IPv6 time servers.