No duplicated IPv6 interface addresses allowed on USG

Robson Posts: 4
First Comment
edited April 2021 in Security

I'm using several VLANs in my network all on underlying LAN1 interface. I try to give each VLAN interface the IPv6 address fe80::1 but the Web GUI does not allow to configure this address. Why? When I'm using CLI it's possible but I can this only do for one interface. When I try to configure the same address to another VLAN interface I get the error that this address is already in use. How can this be? For my understanding, same link-local addresses can be used on different network segments. I want to have each interface in all VLANs using the same simple gateway address. Is this a bug or am I wrong here?

Thank you for your help already.

Kind regards,


All Replies

  • Zyxel_Cooldia
    Zyxel_Cooldia Posts: 1,446  Zyxel Employee
    First Anniversary 10 Comments Friend Collector First Answer

    Hi @Robson ,

    You cannot bind duplicated IPv6 address to different interface/vlan. It will show error message when you create duplicated address. 

    What is your IPv6 address allocation of Lan from ISP? I would suggest use IPv6 Subnetting for lan side hosts.

  • Robson
    Robson Posts: 4
    First Comment


    thank you for your response. I'm getting a /56 subnet from the IPS using DHCPv6 on the WAN adapter. With the help of prefix delegation I use the last 8 bits to create /64 subnets on my VLANs. I'm also using local uniqe addresses (fc::) to have static addresses inside as global addresses are changing and I want hosts having a fixed IPv6 address in the subnets.

    It's not a problem using Router Advertisement to get gateways configured, so there's no need anymore to continue this threat here. Problem was just that Windows clients did not keep the router configuration but in another threat here in the forum I got a link to a firmware which should fix this issue.

    Thank you an best regards,


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