IPv6 DNS took precedence over newer IPv4 assignment

amigan_99
amigan_99 used Ask the Experts™
on
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
Comment
Watch Question

Do more with

Expert Office
EXPERT OFFICE® is a registered trademark of EXPERTS EXCHANGE®
Instructor
Top Expert 2015
Commented:
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.
Top Expert 2014

Commented:
@donjohnston - I think you meant to say, "IPv6 lookups (AAAA) are preferred over IPv4 (A)."
:)
Don JohnstonInstructor
Top Expert 2015

Commented:
Yep.  Strikes again, Dyslexia does. :-)
JavaScript Best Practices

Save hours in development time and avoid common mistakes by learning the best practices to use for JavaScript.

amigan_99Network Engineer

Author

Commented:
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.
Don JohnstonInstructor
Top Expert 2015

Commented:
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.
amigan_99Network Engineer

Author

Commented:
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!
amigan_99Network Engineer

Author

Commented:
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.

Do more with

Expert Office
Submit tech questions to Ask the Experts™ at any time to receive solutions, advice, and new ideas from leading industry professionals.

Start 7-Day Free Trial