Identical IPV6 Addresses in DNS for Different PCs

We just finished installing many new Win 7 PCs.  We imaged and sys-preped each one correctly.  When joining them to the domain we gave them various names until they were permanently placed.  For instance available1, available2, etc.  (See attached image).

Now we are cleaning up AD and DNS of the old PCs and we found multiple identical IPV6 addresses associated with the original “Available” PC names.  ?  The PCs all have unique names and IPV4 and IPV6 Addresses now but these seem to be leftover.  All DC and PC functions are normal.

My question is, is it safe to delete all of these PV6 entries?
Thank you!
TonygretAsked:
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Hypercat (Deb)Commented:
As long as those machine accounts no longer exist on the domain (with the old names, that is), then you should be fine to delete those entries.  If you had the PCs turned off for a period of time, and then turned them on one or two at a time to reconfigure them, depending on your DHCP and DNS settings and scavenging, etc., it's entirely possible that what you described could happen.
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TonygretAuthor Commented:
Hypercat,

I forgot to upload the image.  Take a look and let me know if your answer still applies.  Thanks!
ipv6Adres.JPG
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ZenVenkyArchitectCommented:
Yes, you can safely delete those IPv6 addresses. They are dynamically assigned IPs so if you delete them they will generated with some other PCs. It is happens when IPv6 is configured under DHCP. Also do not disable IPv6 in any machine in the network. For more info check below link.

DNS Best Practices
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Hypercat (Deb)Commented:
As long as these addresses are dynamically assigned, you can safely delete any records that refer to machines that no longer exist or are no longer expected to be connected to your network.  AAMOF, you would want to do this to be sure that you don't run out of IP addresses for your live network.  Even if you delete a record for a machine that's temporarily offline, and then you bring that machine back online, it will simply get a new IP address.  By default, IP addresses assigned through DHCP expire in 8 days if they aren't renewed anyway.

Assuming you have Windows DNS and Windows DHCP, then you would also want to make sure that you go into your DHCP server mgmt. console and remove the leases if they are still showing there as well.
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TonygretAuthor Commented:
Hypercat,

We do not use DHCP for IPV4.  All IPV4 addresses are manually assigned and we have no DHCP server set up.  However the IPV6 addresses I assume are assigened by AD in another fashion.  I admit I am stumped how these IPV6 addresses are assigned. But from what you are saysing it is safe to delete them anway, correct?
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Hypercat (Deb)Commented:
OK, then, what is happening is that the TCP/IP client on the workstations is auto-assigning the IPv6 address to match the IPv4 address you assigned manually.  This happens on all Win7 workstations that have IPv6 enabled, whether the TCP/IP address is assigned by DHCP or manually. It shows up in the ipconfig results as "Link-local IPv6 address."  What I'm not sure about is why you are even looking at the IPv6 addresses in DNS if you're not really using IPv6 internally.

Anyway, it really doesn't make a difference - you can delete the old addresses in DNS (and you WANT to do that so that your DNS zone doesn't get populated with invalid addresses).  You may want to configure DNS scavenging for future reference:

http://technet.microsoft.com/en-us/library/cc771362(v=WS.10).aspx
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TonygretAuthor Commented:
Thank you both very much.  I will enable the stale record scavaging and delete all those entires manully for now.  To answer the question "why you are even looking at the IPv6 addresses"?  It is because we just changed out dozens of PCs and wanted to clean up DNS and found those odd enries. Most of the old PCs were XP and had no IPV6 entires so this was somewhat new to us.  

Thanks again!
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