Re: A common problem with SLAAC in "renumbering" scenarios

[Mark Smith <[e-mail]>]

On Wed., 6 Feb. 2019, 06:01 Richard Patterson <[e-mail] wrote:

> On Tue, 5 Feb 2019, 17:54 Jan Zorz - Go6 <[e-mail] wrote:
>
>> On 05/02/2019 18:28, Richard Patterson wrote:
>> > On Tue, 5 Feb 2019 at 15:41, Jan Zorz - Go6 <[e-mail]> wrote:
>> >
>> >> simply assigns a big IPv6 prefix to that BNG/BRAS as a "pool" where
>> >> BNG/BRAS allocates prefixes to customers "at it's will". It's fast,
>> it's
>> >> simple and works in a lab environment.
>> >>
>> >> That's the behaviour that needs to stop.
>> >
>> > Why?
>> >
>>
>> Here I'll have to repeat what Ole said at the beginning of this
>> conversation. If you setup a lifetime of prefix delegation and assign it
>> to CPE, then CPE expects to get the same prefix back at least for that
>> period of time. That doesn't mean that you can assign prefixes at will
>> at any time you want. You are breaking the "contract" to your customer
>> (CPE). That's exactly the point where things break.
>>
>> If you set a lifetime of assigned prefix to 24 hours and then change it
>> - well, that's your decision, but you are not suppose to break the
>> timers that you set yourself.
>>
>
> That's fine, except it doesn't really have anything to do with your
> previous statement.  I can (and do) assign a single large prefix to each
> BNG for the DHCPv6 server to assign dynamic PDs from, and still respect the
> above assertions.
>
> We use 1 hour lease times.  If a CPE hasn't sent a Release, has the same
> MAC address and DUID, it will continue to get the same PD after a
> [hard|soft]-reboot.  In fact it can return anytime up to an arbitrary value
> (7 days in my network), and still receive the same PD, if the BNG/DHCPv6
> server is configured to keep state for longer.
>
> As just mentioned by Lee, we should be making sure that these protocols
> are resilient to change, not dictating rigid network designs.
>


This isn't the WG that can solve the idenitifer/locator problem.

It's today's primary transport layer protocol that is requiring address
stability for the duration of its connections.

If TCP or some other new transport layer protocol stops imposing that
requirement on IPv6, then PD prefix stability across CPE reboots becomes
irrelevant.