[ipv6hackers] Win7 - no managed flag, DHCP address released?!?

Matej Gregr igregr at fit.vutbr.cz
Mon Nov 12 00:38:35 CET 2012

On 10/18/2012 03:33 PM, Karl Auer wrote:
> [I sent this to the IETF list and they suggested I repost it here.]
> I have just seen the following demonstrated.
> Two routers, short RA interval, both sending RAs for the same prefix,
> both with the autoconf flag set, one with the managed flag set and one
> without.
> A Windows 7 host gets an address via DHCPv6 when the RA with the managed
> flag comes around - and DROPS IT when an RA without the managed flag
> comes past.
> This is not the valid lifetime expiring normally. I was not able to
> determine whether the Windows host is actually sending a DHCPv6 release
> as well, but it is most certainly dropping the address from the
> interface.
> I will be trying to do my own tests to confirm (or not) this behaviour,
> but has anyone else seen it? Or seen it with other operating systems?
> If it is indeed happening, this behaviour seems very badly broken to me.
> I don't feel the relevant RFCs can reasonably be interpreted as
> supporting this behaviour.
> Regards, K.

Hi Karl,
   this is nothing new and yes, it works like you saw. See for example 

The Windows host will send DHCPv6 release if receives a router 
advertisement with M flag off.

Btw, Windows clients, configured with internet connection sharing and 
sending rogue RA, are sending these RA with M flag off and O flag on. 
That basically means, that, if you cannot filter these types of 
messages, it will break the DHCPv6 address assignment in your whole network.


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