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BradleyNorth-7723 avatar image
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BradleyNorth-7723 asked DSPatrick commented

ipconfig /all lists the same IPv6 DNS servers twice

Hi,

This question is purely out of curiosity but could someone explain why one of my windows 10 machines lists the same ipv6 DNS servers twice in ipconfig (see screenshot below). My other machine does not do this.

The IPv4 servers are set to be obtained by the router from my ISP (BT) and the ipv6 servers are specified manually within the router's configuration. There are no DNS servers manually specified within the network settings on the pc.

It does not make any difference when I release or renew the IP addresses or reboot.



110709-ipconfig-all-scrnsh.jpg


windows-10-network
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Did you have any updates on this question?

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DSPatrick avatar image
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DSPatrick answered DSPatrick commented

Might try it on someone else's network for a test. Might also ask in the router manufacturer forums about this. The doubles are google DNS if that helps. Also try setting different ones in the router config for a test.

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Hi,

Yeah I set Google's servers in the router config as BT don't have ipv6 DNS servers, although the ipv4 ones will resolve ipv6 names.

If I set different ones then they are duplicated the same, but only on this one pc.

The other pc just lists each of the servers once as you'd expect. The other pc has a realtek ethernet adapter, I wonder if that'd make a difference.

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DSPatrick avatar image DSPatrick BradleyNorth-7723 ·

Could be, might want to ask the pc or hardware vendor about this. I'd still also test on a different DHCP server to confirm.


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CandyLuo-MSFT avatar image
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CandyLuo-MSFT answered

Hi ,

Based on my understanding, your symptom is that ipv6 servers which manually configured within the router will show twice on your windows client. Is that right? Please feel free to let me know if I have any misunderstanding. In order to narrow down whether the symptom is related with router , as Dave said, you can change to different DHCP server and then see if the symptom still happens.

Best Regards,
Candy


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DSPatrick avatar image
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DSPatrick answered DSPatrick commented

Just checking if there's any progress or updates?

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Sorry I did not come back to this thread. I don't have access to an easy way to test this on another network or change the DHCP server at the moment.

The symptom has persisted on the original machine, and today I noticed that the other one is now doing the same. I have made no changes to any configuration.

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DSPatrick avatar image DSPatrick BradleyNorth-7723 ·

The router's DHCP server is the common between them which makes sense.

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Yes it does make more sense that they are both now behaving the same way.

The only thing I can think of is that the DHCPv6 is set to stateless management, but the DHCPv6 server is also enabled. I don't really want stateless, but if I switch to stateful then Android devices will not get an ipv6 address since they do not support stateful DHCPv6.

I have a debian linux machine as well which strictly obeys the management and only gets a SLAAC address, it ignores the DHCPv6 server even though it is enabled. If I switch to stateful it only gets a stateful address and does not do SLAAC.

Windows however, ignores the management "m bit" and gets both SLAAC and stateful addresses (as well as its privacy extension ones). It might be that it is listing the DNS servers twice, one for the SLAAC and one for the stateful. I will have to see what happens if I turn off DHCP server altogether.

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