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I'm trying to get a NETGEAR R7000 running dd-wrt (DD-WRT v3.0-r35030M kongac (02/19/18)) to serve IPv6 addresses with their complement IPv6 DNS servers.

IPv4 works as expected, and I have modified the configuration to advertise IPv4 DNS servers through this dhcp-option command. I put this into DD-WRT>Services>Services>Dnsmasq>Additional Dnsmasq Options. (image: https://i.imgur.com/iP1EyaA.png)

dhcp-option=6,198.206.14.241,138.197.25.214

Windows fetches the IPv4's DNS addresses successfully.

Connection-specific DNS Suffix   : ***
Description                      : ***
Physical Address                 : ***
DHCP Enabled                     : Yes
IPv4 Address                     : 192.168.1.7
IPv4 Subnet Mask                 : 255.255.255.0
Lease Obtained                   : 2018, May 18 09:56:24
Lease Expires                    : 2018, May 19 09:49:32
IPv4 Default Gateway             : 192.168.1.1
IPv4 DHCP Server                 : 192.168.1.1
IPv4 DNS Servers                 : 198.206.14.241, 138.197.25.214
IPv4 WINS Server                 : 
NetBIOS over Tcpip Enabled       : Yes
IPv6 Address                     : 2601:2c5:c000:4c63:bc0d:9d58:6daf:81cf
Link-local IPv6 Address          : fe80::bc0d:9d58:6daf:81cf%14
IPv6 Default Gateway             : fe80::2e30:33ff:fe44:7029%14
IPv6 DNS Server                  : 

The problem is I cannot get DD-WRT to do the same with IPv6. In the above Windows example, IPv6 has no accompanying IPv6 DNS addresses, not even the router's IP address (router has DNS server as well) is provided. I have to manually append IPv6 addresses to resolve any IPv6 domain names.

This is my radvd configuration under DD-WRT>Setup>IPV6:

interface br0 {
    AdvSendAdvert on;
    prefix 2601:2c5:c000:4c63::/64 {
            AdvOnLink on;
            AdvRouterAddr on;
    };
    RDNSS 2001:4860:4860::8888 2001:4860:4860::8844 {
            AdvRDNSSLifetime 3600;
    }; # does not work?
};

Entire IPV6 configuration: (image: https://i.imgur.com/Jmuvr6a.png)


I plan on using Pihole on a internal DNS server. Pihole works excellently for IPv4 when I set dhcp-option to dhcp-option=6,192.168.1.12 (as in, clients set IPv4 DNS server to 192.168.1.12). IPv6 DNS queries are forwarded, defeating the adblocker.

migrated from serverfault.com May 18 '18 at 23:39

This question came from our site for system and network administrators.

  • DNS servers, regardless of whether they are addressed with IPv4 or IPv6 addresses, can serve both IPv4 and IPv6 DNS. You can use the Google IPv4 DNS servers to get IPv6 addresses from DNS. – Ron Maupin May 18 '18 at 20:51
  • 1
    Microsoft does not support RDNSS before Windows 10 version 1703. If you have a previous version of Windows, it just won't work, full stop. – Michael Hampton May 18 '18 at 23:49
  • @RonMaupin Understood. I decided to modify my configuration and just let Windows (and other clients) internally decided which server to use. So far, adblocking and Google's IPv6 verification all show positive, so I believe my work is done. Thank you! – kaizer May 19 '18 at 17:19
  • @MichaelHampton I only have two Windows 10 machines running 1709, so I believe I'm okay there. I noticed that disabling IPv4 temporarily brings the DNS IPv6 address to the surface. Thus, RDNSS works; Windows seems to prefer the DNS' IPv4 address over IPv6. Thanks! – kaizer May 19 '18 at 17:27
1

@RonMaupin helped me change strategy and just advertise both IPv4/6 DNS addresses to my internal network, rather than force adoption. One client (Apple iPod) lists both DNS addresses, so it seems no force is required.

@MichaelHampton's suggestion helped me realize Windows does accept IPv6 DNS servers through RDNSS; it seems my computer prefers IPv4. I think netsh prefixpolicies may resolve this.


I updated my configuration as follows (I just advertise 1 address for both protocols):

radvd (ipv6) config:

interface br0 {
    AdvSendAdvert on;
    prefix 2601:2c5:c000:4c63::/64 {
        AdvOnLink on;
        AdvRouterAddr on;
    };
    RDNSS 2601:2c5:c000:4c63:2ee0:e9ba:76fe:5dc5 {
        AdvRDNSSLifetime 3600;
    };
};

dnsmasq (IPv4):

dhcp-option=6,192.168.1.12 

Using nslookup, my Pihole server is indeed able to resolve both IPv4/6. Five Filter's Adblock Test runs positive at block ads while Google IPv6 test confirms IPv6 connectivity, which was my goal.


Thanks to everyone for helping resolve this issue! :)

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