Re: [v6ops] A broken promise - "You said PD Prefix Valid Lifetime is going to be X" (Re: SLAAC renum: Problem Statement & Operational workarounds)

Fernando Gont <fgont@si6networks.com> Fri, 01 November 2019 08:16 UTC

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To: Mark Smith <markzzzsmith@gmail.com>, Ole Troan <otroan@employees.org>
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From: Fernando Gont <fgont@si6networks.com>
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Subject: Re: [v6ops] A broken promise - "You said PD Prefix Valid Lifetime is going to be X" (Re: SLAAC renum: Problem Statement & Operational workarounds)
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On 30/10/19 20:38, Mark Smith wrote:
> On Wed, 30 Oct 2019 at 22:02, Ole Troan <otroan@employees.org> wrote:
>>
> <snip>
> 
>> In the case when a requesting router loses a prefix, it can of course signal that to the hosts as proposed in Fernando's draft. But that doesn't solve the general problem, and I'm skeptical to using addressing as a reachability signal. E.g. if the CPE's upstream link flaps, is that enough to trigger deprecation of the prefix? Of course it shouldn't.
>>
> 
> Exactly. Transient network faults are supposed to be survived - that's
> why TCP makes quite a number of attempts at re-transmitting when
> packet loss occurs, rather than just immediately terminating the
> connection.
> 
> When an ISP "flash renumbers" a customer what's really happening is
> that the customer's network layer point of attachment to the network
> is being changed - the customer is being abruptly disconnected, moved
> and re-connected. Possibly that is easy to overlook because the
> customers physical location and their physical link to the network
> doesn't change.
> 
> I think Ole observed that this is contrary to what the PD prefix's
> Valid Lifetime said would be the case. The ISP supplied a PD Prefix
> with a Valid Lifetime of X seconds, and then broke that promise by
> abruptly changing addressing before X seconds. ISPs should be expected
> to live up to their Valid Lifetime promises.

"Hope" doesn't make networks run properly.

In any case, as previously noted, there are multiple scenarios that may
lead to this problem.


-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
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