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IPv6 DNS took precedence over newer IPv4 assignment

Posted on 2014-03-04
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Last Modified: 2014-03-17
Had a strange thing happen.  I have an HP laptop with Win 7.  I got onto the WiFi network at work which is just bridging the data subnet.  But oddly the expected local IPv4 DNS server was not taking priority as viewed by nslookup.  I think that may be my home comcast assigned DNS.  

So the question is:  Can I make IPv4 addressing and assigned DNS always take priority over IPv6?  The way I dealt with the immediate issue was to just disable IPv6 on the wifi nic.  That worked.  But wonder if there's a more subtle approach I could take.


U:\>nslookup
Default Server:  UnKnown
Address:  2001:558:feed::1
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Question by:amigan_99
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Don Johnston earned 500 total points
ID: 39905235
IPv6 lookups (A) are preferred over IPv6 (AAAA).

You can change this behavior though. But it depends on which OS you're running.  

For windows:
http://superuser.com/questions/436574/ipv4-vs-ipv6-priority-in-windows-7

If not, just google "prefer IPv4 DNS IPv6" and add your OS.
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Expert Comment

by:footech
ID: 39905310
@donjohnston - I think you meant to say, "IPv6 lookups (AAAA) are preferred over IPv4 (A)."
:)
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Expert Comment

by:Don Johnston
ID: 39905314
Yep.  Strikes again, Dyslexia does. :-)
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Author Comment

by:amigan_99
ID: 39905443
Seems we're on the right track.  But the issue I was seeing here was somewhat different.  It's not that DNS was resolving to IPv6 addresses.  It's that the DNS server that Windows 7 had decided to use was at an IPv6 owned by Comcast.  And I had never hard set that DNS server in my TCP/IP properties.  In fact I had gone to entirely different network (work) which hands out a v4 IP address and a local v4 defined DNS server.  Yet my system kept insisting on using that IPv6 DNS server despite reboot, despite ipconfig /release and renew and /dnsdflush.  The only thing that worked was going into wifi adapter properties and unchecking the IPv6 box.  Then everything sorted itself out.
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by:Don Johnston
ID: 39906115
I guess I'm not following you.

If there is any IPv6 DNS server, your host will use that to resolve a domain name.  You got the DNS server through DHCP.
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Author Comment

by:amigan_99
ID: 39919703
Oops - hadn't responded in a while.  Following up..

The IPv6 DNS information must have come from my home and not from the DHCP servers at work.  At least that would be a viable theory.  I have Comcast at home so I could see the laptop grabbing an IPv6 Comcast IP and DNS from the Comcast (XFinity) router.  But what I'm saying is - the next day I go into work.  I know that the work networks have no direct connection to Comcast anything.  The DHCP server at work hands me an IPv4 address (and perhaps an IPv6) and yet I still have that comcast IPv6 DNS server.  The DHCP servers at work have no knowledge of that DNS server.  Yet it keeps coming back like a crazy ex girlfriend!
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Author Closing Comment

by:amigan_99
ID: 39935632
I didn't really solve the mystery in full and I don't want to go through the process of recreating the environment with the failed state.  But this is very helpful information for dealing with IPv6 generally in the future.  Thank you.
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