Re: [v6ops] new draft: draft-colitti-v6ops-host-addr-availability

Lorenzo Colitti <> Tue, 07 July 2015 01:19 UTC

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From: Lorenzo Colitti <>
Date: Tue, 7 Jul 2015 10:19:16 +0900
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To: "Fred Baker (fred)" <>
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Subject: Re: [v6ops] new draft: draft-colitti-v6ops-host-addr-availability
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On Tue, Jul 7, 2015 at 9:02 AM, Fred Baker (fred) <> wrote:

> The statement that I don't see in the document, which would help me
> personally, is a problem statement. I would guess that the problem
> statement is "we think some networks are limiting host interfaces to a
> single IPv6 address." I'd want a little more detail, but I'll bet that's
> the crux of it.

Not necessarily "are limiting" today, but "will limit" in the future.

Suppose that all operating systems of interest to a given network support
DHCPv6 and it is thus possible to run a network without SLAAC and without
IPv4 without denying service to substantial percentages of users.

Let's consider what would happen in such a DHCPv6-only network. How many
addresses would be available to each host? Because DHCPv6 requires an
explicit request to the network before an address can be used, the answer
is, by definition, "as many as the network administrators decide to make

In some of these networks, the "as many as the network administrators
decided to make available" may equate to just one. There could be lots of
reasons for this: technical reasons such as "our IPAM and logging systems
support only one address per host and it's tied into our legal intercept
system so we can only give out one address per host", "we only have enough
TCAM entries for one address per host", "one address per host is what we do
in IPv4, and we want to be consistent with that".

If that sounds unreasonable, now consider what would happen in a hotel
network that charges $5 per device. How many addresses would be available
to hosts on such a network? At best, one for every $5 paid. More likely, if
the billing system does not support more than one IPv6 address (why would
it?), the answer would become "one per MAC address".

I hope we agree that such networks provide suboptimal service, and that
there are a number of things that users would like to do that require
either the availability of more than one IPv6 address.

If we are able to agree on that, then it is a useful statement to make, for
two reasons:
1. The network administrators might listen to the statement.
2. Client and server implementations can implement network configuration
protocols such as DHCPv6 in a way that does not lead to this suboptimal