Re: [v6ops] A common problem with SLAAC in "renumbering" scenarios

[Ole Troan <[e-mail]>]

> On 3 Feb 2019, at 05:29, Fernando Gont <[e-mail]> wrote:
> 
> On 2/2/19 08:57, Ole Troan wrote:
>>> One question is whether it makes sense for routers to have valid lifetimes of
>>> more than a day for prefixes that are obtained using DHCP-PD.
>>> 
>>> Another is whether general purpose hosts should accept lifetimes of more
>>> than a day. Maybe hosts should just truncate.
>> 
>> The (original) intended lifetime for DHCP PD is a lifetime equal to the length of the contract with your ISP.
>> Lifetimes become meaningless with “flash renumbering”. Neither SLAAC nor DHCP PD is designed for that.
>> 
>> The simple solution to this problem is “if it hurts, stop doing it”.
> 
> FWIW, lifetimes are mostly irrelevant to the problem that *we* are
> discussing (which is rather orthogonal to the problem mentioned above):
> our case is that in which the router just reboots -- so no matter what
> the lifetime was, the information will be invalid anyway.
> 

That’s not how SLAAC and PD are designed. Lifetimes are not invalid just because of a router reboot. Look at advertised lifetimes as a sort of contract. 

What you seem to be talking about is either a bug a misconfiguration or both. 

With that established, you are arguing that hosts/applications should behave better in the case of this misconfiguration?

If you want something like session survivability,
that’s not a trivial problem to solve.

Currently the network will give an ICMP destination unreachable code 5 and deprecate the invalid prefix if it has information to do so.

Without getting into the multi-homing discussion and requiring hosts to “throw spaghetti on the wall”, I don’t see how your draft improves on that. 

Ole



> Thanks,
> -- 
> Fernando Gont
> SI6 Networks
> e-mail: [e-mail]
> PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492
> 
> 
> 
>