Making IPv6 and OPNsense and Proxmox to work on OVH Cloud.

So I read the article Proxmox + OPNsense + IPv6 and OPNsense/PFsense IPv6 and VIPs – VIPs not routable – OVH network and ran into issues getting this to work.

I found that by running `tcpdump -n ip6` on proxmox I could see Neighbor Sollicitation packets but without an answer for the IP address on the OPNsense router. So at that point I could connect to Proxmox over IPv6 but not yet to OPNsense.

So I was wondering what I needed and then found ndproxy and that closed the gap.

1. Install ndproxy on your OPNsense router as indicated.
2. Put the WAN interface in promicious mode.
3. Configure the ndproxy:
   1. Put you OPNsense MAC address in the “Downlink MAC Address” field.
   2. Copy the IPv6 addresses of the router sending the ‘neighbor sollicitation packets into the “Uplink IPv6 Addresses” field.
   3. Put your Proxmox IPv6 address (and other IPv6 address that do not need to go through OPNsense in the field “Exception IPv6 Addresses” to prevent OPNsense from stealing them.
4. Enable the service and restart the service.

Now you can ping you OPNsense box and all of a sudden get a reply (unless your firewall rules prevent it).

With tcpdump you will now see:

IP6 fe80::fe34:xxxx:xxxx:xxxx > 2001:41d0:XXXX:XXff:ff:ff:ff:ff: ICMP6, neighbor solicitation, who has 2001:41d0:XXXX:XXff:ff:ff:ff:ff, length 32
IP6 2001:41d0:XXXX:XXff:ff:ff:ff:ff > fe80::fe34:xxxx:xxxx:xxxx: ICMP6, neighbor advertisement, tgt is 2001:41d0:XXXX:XXff:ff:ff:ff:ff, length 32

I hope this will help other to get this combination working.