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

Mikael Abrahamsson <swmike@swm.pp.se> Wed, 23 October 2013 09:21 UTC

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Date: Wed, 23 Oct 2013 11:21:05 +0200 (CEST)
From: Mikael Abrahamsson <swmike@swm.pp.se>
To: Mark ZZZ Smith <markzzzsmith@yahoo.com.au>
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Cc: "v6ops@ietf.org" <v6ops@ietf.org>, "draft-liu-bonica-v6ops-dhcpv6-slaac-problem@tools.ietf.org" <draft-liu-bonica-v6ops-dhcpv6-slaac-problem@tools.ietf.org>
Subject: Re: [v6ops] DHCPv6/SLAAC Make Hosts Confusing-//RE: new draft: draft-liu-bonica-v6ops-dhcpv6-slaac-problem
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On Wed, 23 Oct 2013, Mark ZZZ Smith wrote:

> My question was more specificaly about you using "/128", rather than "an 
> address" or "a single address", because I wondered if the DHCPv6 server 
> supplies a /128 prefix length and the host configures a /128 prefix 
> length on the address.

I am not aware of DHCP being able to hand out IA_NA ranges to hosts. I 
only thought it could hand out single IA_NA.

> As you say below, address prefix length doesn't indicate on-link or 
> off-link presence. So I'd expect a DHCPv6 server to hand out single IPv6 
> addresses with a /64 prefix length, as I think that would be more 
> consistent and more expected when the subnet's prefix length is /64.

You're missing the point. There doesn't have to be a /64. DHCPv6 hands out 
IA_NA which is a single address, which might or might not be covered by an 
on-link prefix.

> For somebody with a IPv4 experience, who wasn't aware an IPv6 prefix 
> length doesn't indicate on-link presence, I think the use of a /128 
> prefix length in this scenario would imply that prefix length does 
> indicate on-link presence. Somewhat pedantic perhaps, however I think 
> anything that may give false indications of IPv6's behaviour, when it is 
> different to IPv4's, is better to avoid.

The /128 is on-link (it's bound to that interface), just that most likely 
nobody else knows about it apart from the router (unless it's covered by a 
prefix being announced as on-link).

-- 
Mikael Abrahamsson    email: swmike@swm.pp.se