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Re: there should be a ULA prefix?? [was: A common problem with SLAAC in "renumbering" scenarios]

Tim Chown <Tim.Chown@jisc.ac.uk> Wed, 27 February 2019 19:46 UTC

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From: Tim Chown <Tim.Chown@jisc.ac.uk>
To: Brian E Carpenter <brian.e.carpenter@gmail.com>
CC: Philip Homburg <pch-ipv6-ietf-6@u-1.phicoh.com>, "ipv6@ietf.org" <ipv6@ietf.org>
Subject: Re: there should be a ULA prefix?? [was: A common problem with SLAAC in "renumbering" scenarios]
Thread-Topic: there should be a ULA prefix?? [was: A common problem with SLAAC in "renumbering" scenarios]
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Date: Wed, 27 Feb 2019 19:46:00 +0000
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References: <6D78F4B2-A30D-4562-AC21-E4D3DE019D90@consulintel.es> <019c552eb1624d348641d6930829fd1f@boeing.com> <CAKD1Yr0HBG+rhyFWg9zh0t3mW486Mjx9umjn+CRqAZg4z9r0dg@mail.gmail.com> <20190221073530.GT71606@Space.Net> <CAO42Z2wmB2W52b4MZ2h9sW5E9cQKm-HRjyf--q8C26jezS7LXQ@mail.gmail.com> <a73818d31db7422b99a524bc431b00ed@boeing.com> <CAO42Z2z9-48Gbb_Exf+oWUqDO=axSLpZBtqeDcxkAoFq5OziGw@mail.gmail.com> <CALx6S3624hnGauG1HaSWPMvQw0t2Q5R3gb8W4R8w3kuK7dcrWQ@mail.gmail.com> <1F07F2BB-2F37-4D12-9731-7892DF4E3D88@consulintel.es> <0a582916-af14-bd82-a4cd-002a36f8830b@huitema.net> <67515a73-26a5-3ed0-da88-1a4ce64550d3@foobar.org> <360afa02-cf23-375c-4876-780d3c2aa5ac@gont.com.ar> <CAHL_VyD34V=TRcsCp0DOO9HJNHyy5xkiMQ_cZoBa7zTE4fe5OA@mail.gmail.com> <ead01e0a-9211-7944-88d6-ae8d037c03a8@si6networks.com> <FB8B77EE-CC16-4418-BB5E-D44EE66D6B72@jisc.ac.uk> <29dcc6ed-03f6-3ead-6866-eecbefdf 1483@si6networks.com> <899A1249-D3D9-4824-8B2E-7E950FBB316A@jisc.ac.uk> <m1gya2p-0000HVC@stereo.hq.phicoh.net> <9b7ba4df-41df-2c03-ddca-e15289075bff@gmail.com>
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Hi,

On 26 Feb 2019, at 19:35, Brian E Carpenter <brian.e.carpenter@gmail.com<mailto:brian.e.carpenter@gmail.com>> wrote:

Philip,

On 26-Feb-19 23:33, Philip Homburg wrote:
So given that document is 12 years old, with that default copied from one that
is 21 years old, is an update required?

And if so, to what?

I think this should be updated.

A long time ago, the model was that you would get a prefix from your ISP
and that was the only global prefix on the local network.

So with short lifetimes, if the internet connection would go down for a
relatively long period, there would be no global prefix anymore and hosts
would have to resort to link local to communicate (which obviously fails
if there are multiple subnets).

Some time in the past, the thinking changed and now there should be a ULA
prefix in addition to any global prefixes.

Really? Where do you think that is stated?

I happen to run my CPE with ULA enabled, but I'm not aware of any
recommendation to do so.

RFC 7084 says simply:

"ULA-1: The IPv6 CE router SHOULD be capable of generating a ULA prefix [RFC4193<https://tools.ietf.org/html/rfc4193>]."

So just capability.

RFC 7638 has a "soft" should:

"A home network running IPv6 should deploy ULAs alongside its globally unique prefix(es) to allow stable communication between devices."

And there's draft-ietf-v6ops-ula-usage-recommendations-05, which meanders somewhat, and appears to be a dead draft.

So I think that with a ULA, it makes more sense for a CPE to limit lifetimes
to some multiple of the RA interval.

Why? I don't expect my ULA prefix to change ever. Or do you mean the lifetimes
for globally routeable prefixes?

I read that as prefix lifetimes, not the prefix itself, though the ULA prefix should be persistent.  RFC 7084 says:

"ULA-2: An IPv6 CE router with a ULA prefix MUST maintain this prefix consistently across reboots."

Tim


  Brian

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