On Wed, 25 Mar 2015, Brian E Carpenter wrote:
2. We assume that a prefix delegation or withdrawal from above by
DHCPv6-PD will trigger the appropriate actions by
draft-ietf-homenet-prefix-assignment. But I can't tell from the draft
how that happens. Presumably some process in the relevant CPE does it.
At this time, I do not understand the DHCPv6-PD state machinery to enable
temporal overlap of prefixes so one can achieve a graceful renumbering
event. I wrote this text a while back but never sent it to DHC. Could
someone please help by explaining how to do this temporal overlap using
DHCPv6-PD?
Hi,
For several reasons, there is a need to have overlapping IPv6 addressing
space, both delegated to devices (PD) or addresses (IA_NA), when doing
graceful renumbering. Let's take the following network:
ISP - CPE - HOST1
The CPE requests a prefix using PD, and is delegated
2001:DB8:100:100::/56. it then configures 2001:DB8:100:101::X/64 on its
LAN interface. HOST1 uses DHCPv6 and asks for IA_NA and is assigned
2001:DB8:100:101::Y/128
IA_NA by CPE.
Now, after a while, the customer decides he wants to change the addressing
space, but he wants to do this gracefully, basically along the lines of
RFC4192. So for a certain amount of time, he wants to have two PDs,
and these need to be distinct.
What would need to happen, is that the customer needs to signal to the ISP
that he needs a second PD, that this should be distinct from the first
one, and that he wants to keep both for a certain amount of time, but
understands that the initial PD is not going to be refreshed/extended in
time and will be removed.
What needs to happen is that the CPE needs to get a new /60, it needs to
allocate a /64 out of this in addition to the existing /64, HOST1 needs to
understand that it should ask for a new IA_NA and that it should stop
using the existing IA_NA for new connections. I don't know if this
automatically happens if the RA for the old prefix shows up with a lower
preferred timer set.
So there are two issues here (I guess):
How can the CPE indicate that it doesn't want the original prefix any
more, request a new one, and let old one expire after a period of overlap?
How will HOST1 understand that it needs to request a new IA_NA while still
keeping the old IA_NA until it expires, and de-preferring the old IA_NA in
the meantime?
Also, how can the ISP initiate this kind of graceful renumbering event?
The only way I can think of would be some kind of intent flag to say "the
lease time of this resource will not be extended and you should ask for
a new one" or something to that effect.
--
Mikael Abrahamsson email: [email protected]
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