Re: [v6ops] DHCPv6/SLAAC Make Hosts Confusing-//RE: new draft: draft-liu-bonica-v6ops-dhcpv6-slaac-problem

Mark ZZZ Smith <> Tue, 29 October 2013 19:28 UTC

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Date: Tue, 29 Oct 2013 12:28:12 -0700 (PDT)
From: Mark ZZZ Smith <>
To: "Weil, Jason" <>, "Liubing \(Leo\)" <>, Wuyts Carl <>, "" <>
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Subject: Re: [v6ops] DHCPv6/SLAAC Make Hosts Confusing-//RE: new draft: draft-liu-bonica-v6ops-dhcpv6-slaac-problem
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----- Original Message -----
> From: "Weil, Jason" <>
> To: Liubing (Leo) <>om>; Wuyts Carl <>om>; "" <>
> Cc: "" <>rg>; "" <>om>; "" <>
> Sent: Wednesday, 30 October 2013 1:44 AM
> Subject: Re: [v6ops] DHCPv6/SLAAC Make Hosts Confusing-//RE: new draft: draft-liu-bonica-v6ops-dhcpv6-slaac-problem
> Leo,
> First I wanted to say this is useful work and I support it.
> This topic in this email reminds me of an issue that we have run across
> that might be relevant to your draft:
> The use case involves a home network whose gateway router sets M=1 and A=1
> in order to provide DHC and and SLAAC for hosts that do not implement a
> DHC client. If the DHCPv6 Server is implementing IP assignment using
> interface-identifier and using the same prefix as advertised in the PIO
> (assuming the server resides on the router advertising the PIO) with the A
> bit set, hosts that support SLAAC and a DHCPv6 client could construct the
> same address using DHC as the one they construct using SLAAC. What is not
> clear is what hosts should do in this situation. IMO, there is a benefit
> if hosts that support both SLAAC and DHCPv6 construct the address and
> prefer the DHC address over the SLAAC address. The benefit is that you
> reduce the number of active addresses and all hosts end up with a single
> address per prefix administered in this fashion.
> Of course if your DHC Server implements another assignment algorithm (e.g.
> Random) then your hosts that support both may end up with 2 addresses out
> of the same prefix.

Another way to describe your scenario is that it is a transition scenario between SLAAC and stateful DHCPv6, since some of your hosts don't support stateful DHCPv6.

In your scenario, I don't think it is a big problem that some of your hosts will have two addresses within the same prefix - IPv6 hosts are designed to cope with many addresses, and a /64 has plenty of addresses to go around.

If you do want to be specifically selective about which hosts use SLAAC and which hosts use stateful DHCPv6 for addressing, use host specific RAs which set the M and the PIO A bits on a selected host basis.