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We have a Windows Server 2012 domain. The server acts as our DHCP and DNS. About 2 weeks ago, Comcast changed something in their router I believe, enabling IPv6. Since IPv6 was never initially set up on our Windows 2012 server, the router was now acting as DHCP for IPv6 addresses. Because of that, none of our pc's in the domain could resolve names since it was no longer using IPv4 and our own DNS server.

I found the setting in the Comcast router to turn off IPv6 DHCP, but it appears the damage is already done. I don't know anything about IPv6 and am the "pseudo" IT guy in the office. I've had to go to all the affected machines and ran "ipconfig /release6" as well as remove all the IPv6 DNS entries on our Windows 2012 Server.

This seemed to "band-aid" the situation, but client machines keep getting IPv6 and DNS keeps getting screwed up.

Can anyone lend some advice on what the problem is and how to solve it?

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    No we are Comcast Business class
    – Snarfblatt
    Dec 10 '14 at 19:47
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    Hm. You should have received a notice that IPv6 was going live, ahead of time, so that you could prepare for it. Anyway, you may as well just sort out the actual problem; you're going to need IPv6 soon enough anyway. Unfortunately you didn't really describe the actual problem. Dec 10 '14 at 19:49
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    @MichaelHampton I'm sure the problem is that the router has stateless autoconf configured (our new Comcast Business modem did) and the clients are preferring the IPv6 configuration, including mDNS addresses or Comcast DNS server, over their internal IPv4 scheme, including DNS on their server.
    – Chris S
    Dec 10 '14 at 19:53
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    @Zoredache Comcast only does dynamic prefix allocations, and only by DHCPv6; and Windows doesn't support that, so... yeah.
    – Chris S
    Dec 10 '14 at 20:15
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    @EEAA, I meant that the Windows DHCPv6 Server can't get it's prefix from DHCP-PD. Windows can pickup an address from a DHCPv6 server or SLAAC.
    – Chris S
    Dec 10 '14 at 21:37
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Band-aid: Login to your modem and disable IPv6 Stateless and Stateful (DHCPv6) Auto-configuration. Also check that DHCPv4 isn't enabled, it's enabled by default. This will just leave you without IPv6 support.

As Michael mentioned above, IPv6 isn't required by very many websites yet, but with IPv4 exhaustion really happening right now (like you can't get IPv4 addresses in parts of the world anymore), there will be more and more IPv6-only sites in the near future.

The "real solution" is to setup DHCP on the router instead of the Server. Windows doesn't play very well with IPv6, at least it's DHCPv6 is "lacking". So you'll run into quite a few problems using it as the DHCPv6 server. The problem with setting up the router as the DHCPv6 server is that you'll lose AD Integrated DNS updates. This can be configured around, but isn't easy. So my suggested "real solution" is to call a local consultant who can configure everything for you.

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    A few parts of what I manage are already IPv6-only. And simply having IPv6 has its own advantages, like being able to get rid of the jumpboxes, simplifying VPNs, etc. Dec 10 '14 at 20:11
  • I should note: I really hate my own answer here, but the EXTREME lack of IPv6 support in Windows hamstrings what I can honestly suggest people try to setup.
    – Chris S
    Dec 10 '14 at 20:13
  • You will lose integrated DHCP updates but not systems that register themselves in DNS with an AD integrated zone.
    – Jim B
    Dec 10 '14 at 21:31
  • Thanks @ChrisS I think I may have to call someone. I'm over my head here.
    – Snarfblatt
    Dec 10 '14 at 21:55
  • I agree with the IPv6 support, its unfortunately similar to FreeBSD.
    – Jim B
    Dec 12 '14 at 6:37

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