Proxmox VE Detected as an IPv6 Router and Neighbor Discovery not working

[silverstone]

On one Linux Client, ip -6 neighbor lists the Proxmox VE Host(s) as Router, when they clearly are not:

2XXX:XXXX:XXXX:1::A:B dev eno1 lladdr 11:22:33:44:55:66 router REACHABLE

Setting sysctl -w net.ipv6.conf.vmbr0.forwarding=0 on the Proxmox VE Host fixed that, but I wonder if that also caused some unwanted side EFfects.

I read the following Topics but their fixes don't seem to help me:
- https://forum.proxmox.com/threads/no-ipv6-on-host-but-all-vms-have-working-ipv6.115995/
- https://forum.proxmox.com/threads/i...r-dedicated-server-running-proxmox-ve.138595/
- https://forum.proxmox.com/threads/multicast-issues-including-ipv6-neighbor-discovery.121476/

I also tried to set sysclt -w net.ipv6.conf.vmbr0.accept_ra=2 but that didn't seem to make a Difference.

I implemented this /etc/network/interfaces but the Issue persists:

bridge-mcsnoop no
bridge-mcquerier yes

Note that the Issue might (also) be caused by some Switch across the Path. It seems Neighbor Discovery works in one Room (on the same Mikrotik Switch), but going to another Room through several Mikrotik Switches and some OpenWrt-flashed Netgear Switches seem to cause Issue and no IPv6 Device gets detected from the other Room.

The main Issue I have is adding Static Routes:

ip -6 route add 2XXX:XXXX:XXXX:AAAA::/64 via 2XXX:XXXX:XXXX:0001:0000:0000:000A:000B metric 256
RTNETLINK answers: No route to host

But of course the Host 2XXX:XXXX:XXXX:0001:0000:0000:000A:000B is correctly on the same LAN Segment / Subnet 2XXX:XXXX:XXXX:0001/64 as my main LAN, I can ping, curl -6 https://<myhost>:443 using TCP, etc

I don't know exactly how ND works to be honest, so I don't know:
- If it's an Issue with the Switch(es): Mikrotik and OpenWrt-flashed Netgear Switch
- The main Router (OPNSense) in the Other Room
- The Network Device (NIC) itself on one or several of the Hosts
- All involved Linux Bridges across the Path
- Proxmox VE Hosts (which are all acting/being detected as IPv6 Routers by ip -6 neighbor unless I do sysctl -w net.ipv6.conf.vmbr0.forwarding=0)
- Something else entirely

Neighbor Discovery on the Linux Hosts lists MAINLY fe80:: Link-Local IPv6 Addresses, with a few Unicast 2XXX: IPv6 Addressees as well.
Mikrotik Switch lists ONLY Neighbors with fe80:: Link-Local IPv6 Addresses.


Network Diagram is quite Complex (and Temporary), but something along the Lines of:

2 x PVE Hosts + 1 x Ubuntu Client <--> Living Room
1 x Mikrotik Switch CRS309-1G-8S+ <--> 1 x Mikrotik Switch CRS309-1G-8S+ <---> Cat 5e Cabling in the Loft <---> 1 x Mikrotik Switch CRS317-1G-16S+ <----> Proxmox VE Host <---> OPNSense Router

On the Mikrotik Switch I tried setting Accept Router Advertisements = yes (before it was only if not forwarding, and forwarding was enabled, thus Router Advertisements were NOT accepted)