Re: [v6ops] Stateful SLAAC (draft-ietf-v6ops-unique-ipv6-prefix-per-host)

Ole Troan <otroan@employees.org> Fri, 10 November 2017 21:52 UTC

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From: Ole Troan <otroan@employees.org>
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Subject: Re: [v6ops] Stateful SLAAC (draft-ietf-v6ops-unique-ipv6-prefix-per-host)
Date: Sat, 11 Nov 2017 05:52:37 +0800
In-Reply-To: <e7465ac9-731f-f41b-c240-f2d9fd6e3c59@si6networks.com>
Cc: Brian E Carpenter <brian.e.carpenter@gmail.com>, v6ops@ietf.org, "6man@ietf.org" <6man@ietf.org>
To: Fernando Gont <fgont@si6networks.com>
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>> I think you also make a point that there are further considerations
>> here, than just the wire-format. Especially around additional state
>> in the routers. In the early days of IPv6 design a lot of time and
>> effort was made in avoiding state in the network. If this mechanism
>> made address allocation inherently less robust, I think a case could
>> be made for why the IETF should specify this in more detail.
> 
> Indeed it does:
> 
> Current SLAAC: Router crashed and reboots -> network doesn't break
> 
> This document: Router carshes and reboots -> who knows what happens.
> (Not only this protocol requires state that wasn't required for SLAAC,
> but now you also need the mappings to be maintained on stable storage.
> Otherwise, if the router crashes and reboots, the netwoks will most
> likely break).

If you read this document as an operational document, describing one potential deployment scenario, then those considerations are left as an exercise to the operator. I.e. don't deploy this in cases where this can happen.

If this has been a protocol specification, I agree that would not be acceptable.

>> I am not convinced of that though. (In my implementation per host
>> prefix adds configured state, but dramatically lessens dynamic state
>> (ND)).
> 
> What do you mean by "configured state"?
> 

In SLAAC, routers require that the IPv6 prefix is configured on the interface.
You can also implement this mechanism in that way.
It is still state, but different dynamically discovered state like the ND cache, or dynamic and non-recoverable state like what you get with middleboxes.

Best regards,
Ole