Hello, this is the situation: In my lab environment I set up Windows 2008 R2 as only DC, DNS and DHCPv6. IPv6 on the LAN interface is manually configured: netsh int ipv6 add route prefix=fdaa:bbcc:ddee:1::/64 interface="LAN" nexthop=:: publish=yes netsh int ipv6 set interface interface="LAN" forwarding=enabled advertise=enabled nud=enabled routerdiscovery=enabled managedaddress=enabled otherstateful=enabled All clients were able to recieve an IPv6-address in fdaa:bbcc:ddee:1::/64 scope. Now a AVM Fritz!Box had to join as IPv6 router. If you enable IPv6 on this device it automatically starts to send router advertisments. You cannot disable this. Now this advertisments leads to following situation: If a client sees an advertisment from server first, it does DHCPv6 and recieves all information needed (internal DNS, DNS search domains). Then advertisment of fritz box follows and it sets my ULA address to "deprecated" and client drops my internal DNS out of its configuration. If a client recieves an advertisment from fritz box first, it will never configure for my ULA. I can configure fritz box to advertise my ULA but this still leads to loss of my internal DNS in client's configuration My question is: How can I get a co-existance, so my ULA won't be deprecated and/or my internal DNS is getting kicked out of client's configuration. Manual DNS configuration on all clients isn't an option. Thanks for your suggestions. Martin