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

Owen DeLong <owen@delong.com> Tue, 12 November 2019 04:17 UTC

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From: Owen DeLong <owen@delong.com>
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Date: Mon, 11 Nov 2019 20:16:38 -0800
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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 Nov 11, 2019, at 00:52 , Philip Homburg <pch-v6ops-9@u-1.phicoh.com> wrote:
> 
>> Why do you think that this "strategy" exists in IPv4 deployments?
> 
> One way to end up in this scenario is to have a pool of IPv4 addresses in
> the access router. A redundant access network makes it possible for 
> customers to end up on different access routers.
> 
> So when the CPE reboots, the line goes down, and the customer gets assigned
> to the best access router. If that is a different one from before then
> the customer experiences flash renumbering.

Does anyone actually do IPv4 this way? I am not aware of anyone. To my knowledge,
the two most common IPv4 multihoming scenarios are:

1.	Public addressing of hosts using an RIR-issued prefix or a prefix from one
	provider routed to two providers via local BGP announcement.

2.	An external address (pool) from each provider which is used for source NAPT
	of outbound packets from internal hosts using RFC-1918 or similar addressing.

Neither of these scenarios has the issue described. In scenario 1, there is no
such thing as renumbering without notice.

In scenario 2, renumbering affects only the outbound NAPT router(s). Sessions may
be dropped in a failure, but retries will receive different external source addresses
via NAPT and be routed via said alternate provider.

>> Why is it relevant and preferable today for IPv6?
> 
> We want to make it easy for ISPs to turn on IPv6. If we first make them 
> redesign their networks then it will be more costly and take more time,
> so there will be less IPv6.
> 
>> Why is it best for IPv6 when people get something different in IPv6 than in
>> IPv4 - public address space to use on their LAN.
> 
> It doesn't have much to with wether addresses are public or not.
> Flash renumbering happens with public IPv4 addresses.

This hasn’t been my experience. However, if the prior poster can’t understand
the benefits of end-to-end addressing in IPv6 vs. the lack thereof in the majority
of IPv4 deployments, then it’s difficult to know where to start in explaining it.

Owen