IPv6 DHCP-PD – Multiple Prefixes Assigned to Same Interface



  • I encountered a very nasty problem a couple of days ago.  Since I was not able to stabilize the network, I ended up re-imaging back to 2.1.5.  So, the problem box no longer exist to collect anything further.  However, I think it is important to document what happened in case it hits somebody else.

    Configuration

    2.2-BETA - Build date was around OCT-14th
    SuperMicro A1SRi-2758F  (this has quad-NIC)

    WAN: IPv6 DHCP-PD /60
    LAN:  Prefix 0 - "3a0"
    DMZ:  Prefix 1 - "3a1"

    NOTE:  The physical network makes it impossible for any "looping" between the LAN and DMZ.

    This configuration has been working fine for several months on 2.1.5 and for over a week on 2.2-BETA before it went crazy.

    Problem

    LAN computers experienced slow or no response from websites.

    Observation

    In ADDITION to the expected 3a0 LAN IPv6 prefix, LAN clients were also getting 3a1 DMZ prefix addresses.

    Here we see that a Windows machine is getting both prefixes.  Mac clients showed same.

    Here we see that DHCPv6 is handing out addresses for both networks to the SAME client.
    Side note:  Why does DHCPv6 function for dynamic networks, but there are no configurable options?

    Troubleshooting

    Verified that the LAN was configured for Prefix 0 and DMZ Prefix 1.

    When I shutdown the DMZ interface and rebooted clients,  they were just on the 3a0 network and worked fine.  Enable the DMZ interface and the 3a1 network appeared again.

    Exact trigger undetermined.

    Reboots did not help.

    Conclusion

    My amateur theory is that radvd (?) "lost it's brains" and started advertising both active prefixes on the same interface.  But then, why did reboots not help?  This was working fine for over a week and then went bad.