Re: [homenet] Let's make in-home ULA presence a MUST !?

Ted Lemon <mellon@fugue.com> Fri, 17 October 2014 13:29 UTC

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From: Ted Lemon <mellon@fugue.com>
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Date: Fri, 17 Oct 2014 08:29:28 -0500
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To: Lorenzo Colitti <lorenzo@google.com>
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Cc: "homenet@ietf.org" <homenet@ietf.org>, Michael Thomas <mike@mtcc.com>, "STARK, BARBARA H" <bs7652@att.com>
Subject: Re: [homenet] Let's make in-home ULA presence a MUST !?
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On Oct 17, 2014, at 1:35 AM, Lorenzo Colitti <lorenzo@google.com> wrote:
> You keep mentioning this, but you're incorrect. Even if the ISP flash-renumbers, hosts will not lower the lifetime of their IP addresses below 2 hours, per RFC 4862.

You are technically correct, and I will admit to having gone slightly into the weeds there, but let me remind you of how this conversation started: someone again proposed that we retain a stale GUA rather than having a ULA.   So if you go offline and then come back online, your stale GUA gets flash-renumbered even if your ISP doesn't have a policy of doing flash renumbering.   When I say it gets flash-renumbered, I mean that the ISP is no longer offering service on that GUA, regardless of whether hosts may still consider it valid.

Why do we care?   Because you are now advertising an invalid GUA on the homenet.   Hosts will think that they can use that GUA to communicate _off_ the homenet, and lossage will ensue.   Apps that do happy eyeballs will be less affected by this, but not all apps do happy eyeballs.   So when the upstream gets flash renumbered, you _really want_ to tell hosts on the local network that that prefix has a valid lifetime of zero, so that they don't mistakenly use it for communication off-homenet.

And then there's the long-lived connection _in_ the homenet.   If we insist on using non-stable GUAs, then my ssh connection to my home server, which I often do keep open overnight doing something, would be killed by the renumbering that has to happen when the upstream is renumbered and there is no stable ULA.   For those who still do X windows, any of their X window connections to hosts on the homenet would be dropped.

So this is why I am arguing that homenets SHOULD have ULAs, and why Markus is arguing that they MUST.   We really do want hosts to prefer the ULA if they can use it, and we really do want to always have a ULA.   Hosts that are communicating on intra-homenet should not be using GUAs to do so, and it is worth a little effort to try to ensure that that is the case.