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I'm playing with Windows 2012 DHCP server for IPv6. As with IPv4, the client network interfaces can be configured to either obtain an IPv6 address automatically, or use a statically configured address.

However, what I observe is that even for those hosts where I configured a static IPv6 address, they additionally acquire a DHCP address. This is even the case for the DHCP server itself!

How come?

Hagen von Eitzen
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1 Answers1

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The automatic address is from stateless address configuration. If you want to use stateful (with static addresses) configure your router to turn off the autonomous flag and turn on the manual flag. Some people say to turn on the other flag, literally called 'other' flag. I don't know what this does but setting the manual flag and autonomous flags work for us.

If you run get-netipaddress in powershell it will tell you the origin of the addresses.

This question gets asked a lot and seems to be a common misunderstanding of how IPv6 works.

What is really crazy is when the manual flag and autonomous flags are both on, then the server has about 4 addresses; DHCP assigned stateful, DHCP stateless, link, and static.

UpTide
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  • Yes, most of the time I think IPv6 is just a more-bits version of IPv4 :) `get-netipaddress` tells me that the origin of th addresses is dhcp, which I alreday knew. - Not sure what my router has to do with it, it does not have IPv6 activated (yet) – Hagen von Eitzen May 21 '15 at 18:13
  • Upon second thought I think the real question behind my question is: Would it be safe / useful /best practice to simply let even the DHCP server itself acquire its address solely voa DHCP (so from itself) without there being a bootstrapping conundrum ... ? – Hagen von Eitzen May 21 '15 at 18:24
  • We do not for the same reason we assign a number to the gateway despite the gateway only using local link. If something happens to DHCP/DNS we want the server to still be online, something that can't be assured with DHCP stateless or autonomous addressing (as in DNS doesn't work so we can enter the IPv6 address into RDP). It also allows the DNS announcement from DHCP to be accurate, which is most likely the important thing. – UpTide May 22 '15 at 15:26
  • What flags do you have turned on? – UpTide May 22 '15 at 15:32
  • At the risk of sounding stupid, but I'm getting more confused by the minute. I don't see flags anywhere. After reading a bit, it seems that these flags should come with a prefix information option (26) in DHCPv6. No such option can be configured for server or range on my Win2012 DHCPv6 server, and in fact the option would mostly correspond to the range itself anyway and the range properties are: preference, some dynDNS related stuff, preferred/valid lease time. There is no such thing as "autonomous" or "manual" or "other" there. – Hagen von Eitzen May 22 '15 at 16:38
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    The whole DHCP idea has changed with IPv6. The network is configured to either be stateful, stateless with DHCP, or stateless without DHCP. The flags that control the network 'state' if you will, are on the router; Windows has about 0% to do with the 'state' in a _normal_ setup. There are ways to manually make Windows advertise these but it isn't the way it should be. With IPv6 you must have a router along with a DHCP server to make a network. – UpTide May 22 '15 at 18:10
  • Flag M or manual tells the client that it needs to get an IP address from the DHCP server, no more. Flag O or other tells the client to get 'other' information from the DHCP server (like DNS and domain prefixes and time servers). Flag A or autonomous tells the client it needs to use its MAC and make its own address to use on the network. – UpTide May 22 '15 at 18:13