Server not pingable over IPv6-address

[RubenPortier]

I've been having a strange issue which I can't seem to fix for a long time now. I'm using an old computer with PFSENSE as my main router which has a switch connected to it. This allows me to use my two Asus AC-66U's as AP in my house. The router is configured with both a public IPv4 adres and a public IPv6 subnet (56 prefix length).

I've also build a server (with old computer hardware ) which runs multiple virtual machines. Some are for development (websites and Python apps) and one in particular is for my homeserver (storage of files, back-ups etc.). Since I got an IPv6 subnet from my ISP I've been having troubles with connecting to this server and all of its VM's. I have the host and the guests (VM's) set-up to use a static IPv6 address in the IPv6 prefix range. They all work fine and can connect to the internet. All my LAN devices can also ping the servers without any problems. However, my Macbook Pro (and all my LAN wireless connected devices) will not be able to ping any of the servers after waiting a couple of minutes from the last ping (or any other type of connection to the server). Each server is having its own "time", what I mean by that is if I ping the host and then stop, after approximately 5 minutes when I try to ping it again it will fail. I can still ping guest1, but when I also wait 5 minutes, it will also not be working anymore. Server servers itself are still able to ping any device or IP address (even public ones) but the Wi-Fi device that is trying to ping it.

I have no idea if this is hardware related to the server (as I have tried with a live Ubuntu USB and it didn't seem to have any problem), a bug in the Asus-WRT firmware, a misconfiguration somewhere, or my Wi-Fi devices (which would be weird, because then all of them would be faulty?). I've done some testing by looking at the IPv6 ICMP packets send while trying to ping the server and it's failing. I can see that the client (My Macbook Pro or any other Wi-Fi device) is sending out a neighbor solicitation (ND) to the server. The server is actually receiving this and sends back a neighbor advertisement. The thing is, I can not see any receiving advertisement on the client, which causes the ND to fail.

I know there are some problems with IGMP Proxy which faultily filters some ICMP6 packets causing problems with ND, but I've turned IGMP proxy off on both AP's and the server. I've asked for help an multiple forums, but none seem to be able to help me any further. I don't think this is an issue with the AP's, but as both my AP's are the exact same model and firmware, there still could be some relation to this. I also can't see any advertisement on the AP on which the server is connected to (via UTP-cable), so I think it's not even reaching the AP. I just hope someone here can help me dig a little further about what my problem could be. I could try a reinstallation of Ubuntu (the servers OS), but I've upgraded recently and it did not fix anything. I know it's a lot to read and I'm asking for a lot, but It's very frustrating while developing a website and not being able to open it in the webbrowser, as I cannot longer reach the server at a certain time. Also worth mentioning is that when I ping the server over its IPv4 (local) address, the ND starts working again and I can work again for a little while.

 

[RubenPortier]

I can now confirm that this is a router related issue. I've tried a different AP (an old Apple AirPort Express with only b/g support) and it's working! When I switch between the AP's the Asus router does not work (not able to ping my server over IPv6), but using the AirPort it keeps working! I will now try setting the AP's back to router mode with DHCP server disabled, maybe something is wrong when using the router in AP mode?

I would love some help on this matter!

EDIT:

I think this could be related to MLD snooping being enabled on the wireless bridge? I'm not sure how I could check that and even turn that off? I can see the wireless client is sending neighbor solicitations to the server, which then arrive on the router (AP) and then go to the server. The server is responding with a neighbor advertisement, but this is not visible on the br0 of the AP. Why is this?

 

[RubenPortier]

I've tried using a different network card, still same problem. I'm 100 % sure it's the AC66U I use as AP's, as when I ping the local IPv4 address of the serves on the specific AP (router) the wireless client is on, it start working again. Also, the Neighbour Advertisement is send from the server to the client, so it must be the router not sending the packet to the wireless client? I really hope someone could help me out here. I've tried multiple firmwares, even the stock Asus.