IPv6 SLAAC addresses mixed up in subnets

  • Hi there!

    When rebooting my pfSense, the clients on the subnets are getting SLAAC addresses from the connected and also the neighboring subnets. This phenomenon only occurs during reboot.

    I have a /56 subnet from my ISP which I am splitting up in 7 subnets (/64) for my private LAN which are connected via a LAN interface with 1 untagged and 6 tagged VLANs.

    All LAN interfaces are configured as DHCPv6 with router mode Managed - RA, so there shouldn't be any SLAAC, I assume.

    My pfSense is running on a Hyper-V host (Windows 2016) and is connected to a Hyper-V switch internally via trunk port for the LAN. The physical NIC is a Intel X550-T2. The VLANs are configured in the pfsense setup and I had the same phenomenon when assigning multiple virtual NICs to the pfsense and tagging them in Hyper-V and attching them to the switch as Access ports instead of trunk.

    I tried narrowing down the problem by disabling the offoading items under Advanced -> Networking and also experimented with different settings for the physical NIC but wasn't successful there.

    Does anyone have some ideas on where to look for the configuration error?

  • @normand

    Any chance you have a TP-Link managed switch? Leakage between VLANs is a known problem with some models.

  • No, Netgear and HP. All managed.

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