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

Jan Zorz - Go6 <jan@go6.si> Tue, 05 February 2019 10:41 UTC

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Subject: Re: A common problem with SLAAC in "renumbering" scenarios
To: ipv6@ietf.org
References: <60fabe4b-fd76-4b35-08d3-09adce43dd71@si6networks.com> <alpine.DEB.2.20.1901311236320.5601@uplift.swm.pp.se> <m1gpCcz-0000FlC@stereo.hq.phicoh.net> <ddd28787-8905-bafd-3546-2ceef436c8b0@si6networks.com> <m1gptWx-0000G3C@stereo.hq.phicoh.net> <69609C58-7205-4519-B17A-4FBC8AE2EA16@employees.org> <d40b41c3-ff1b-cab4-a8de-16692a78e8fd@go6.si> <D1E45CAD-08D0-43D4-90F7-C4DD44CB32C0@employees.org> <alpine.DEB.2.20.1902041330531.23912@uplift.swm.pp.se> <62b74cf1-9cb0-bba3-b078-cb6f48e90145@foobar.org> <m1gqeb9-0000GCC@stereo.hq.phicoh.net>
From: Jan Zorz - Go6 <jan@go6.si>
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Date: Tue, 05 Feb 2019 11:41:20 +0100
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On 04/02/2019 14:47, Philip Homburg wrote:
>> Unless I'm mistaken, Ole is saying that a dhcp6-pd lease for time period
>> X is a contract for time period X, during which the ISP should retain
>> enough state that if the CPE issues another dhcp request within time
>> period X, they will receive the same prefix.  However, when time period
>> X elapses, the ISP is fully within their rights to assign a different
>> prefix.
> 
> The way I understand DHCP leases is that for the duration of the lease,
> the party that obtained the lease has exclusive use of the address or prefix.
> So it is a requirement on the DHCP server to avoid giving the lease to another
> party.
> 
> As far as I know it never said anything about getting the same address or
> prefix if you do a DISCOVER.

That seems to be the core of the problem, me think :) BRAS-es with 
defined IPv6 pools assigning PD-s randomly, regardless of anything and 
everything.

> 
> A related point, and that's where it starts getting complicated, is that
> over time DHCP got used for access control. Initially DHCP was just a way
> for making sure that everybody got a unique address, but you could just
> use any address you liked at the risk of collision.
> 
> These days access routers restrict source addresses to whatever was offered in
> a DHCP lease. And this is where it gets messy.
> 
> In theory we could specify how access routers could do the right thing. And then
> get CPEs to do the right thing as well.

I'm starting to think that we should make all 3 places (access router, 
CPE and host) more robust and binding to some defined standard.

Cheers, Jan

> 
> But I think it would be more productive to make hosts more robust.
> 
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