I have a pFsense machine running as my main router. A switch is connected to the ethernet out of the machine which connects to multiple devices. All those devices receive their IPv4 and IPv6 address from the router. I also own 2 Asus AC66U's which are both configured in the AP (Access Point) mode. They act as a switch and send out both 2.4 and 5 GHz WiFi. I also have a homeserver that is connected wired to the switch, which also has an IPv4 and an IPv6 address (static).
My network is working fine without problems, I can reach both IPv4 and IPv6 addresses, and alls local devices are accessible via their local IP address. My real problem however is when I have a client connected using WiFi on any of those two AP's, I cannot reach the server over IPv6. The ND (Neighbour Discovery) is failing only when connected over WiFi and only when connecting to that specific machine (homeserver, running Ubuntu 16.10). I've tried multiple version of Ubuntu, multiple NIC configurations etc., none seem to be working.
The weird thing is, when I reboot my device that is wirelessly connected I can ping the server over it's IPv6 address. But after a short while, the Neighbour Discovery starts failing and I can no longer reach that server as long as I do not reach it over it's IPv4 address. As soon as I ping or ssh with the servers' IPv4 address, the ND is working again, but only for a short while, and it eventually repeats.
I've been doing some research and I can see the server is receiving NS (Neighbour Solicitation) from the wirelessly connected device and is sending back a NA (Neighbour Advertisement). When I use tcpdump on the AP, I can see the NS, but the NA does not arrive. I have no idea wether this is at fault at at the AP or at the server. It's also strange that it's working fine when I'm connected via wire.
I'm running the latest Merlin Firmware and have tried multiple versions. I made multiple bug reports and forum threads on both the official Asus forum as the Forum where the custom firmware for Merlin is discussed and no one seems to be able to help me nor do I get replies. So this is a last resort to fix this issue, as it's very annoying.
I can give more information when needed, and am willing to change one of the AP to other firmwares etc. I think I need to look into the AP's as it's the only thing that actually makes the difference between wireless and wired and the NA does not arrive there.