Re: on-link and off-link addresses, side discussion
Philip Homburg <pch-ipv6-ietf-7@u-1.phicoh.com> Thu, 08 July 2021 14:18 UTC
Return-Path: <pch-b9D3CB0F5@u-1.phicoh.com>
X-Original-To: ipv6@ietfa.amsl.com
Delivered-To: ipv6@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 9C2843A1DE6 for <ipv6@ietfa.amsl.com>; Thu, 8 Jul 2021 07:18:56 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.896
X-Spam-Level:
X-Spam-Status: No, score=-1.896 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_NONE=0.001] autolearn=ham autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 1kVIzXlAtmJD for <ipv6@ietfa.amsl.com>; Thu, 8 Jul 2021 07:18:53 -0700 (PDT)
Received: from stereo.hq.phicoh.net (stereo.hq.phicoh.net [130.37.15.35]) (using TLSv1.2 with cipher ECDHE-RSA-CHACHA20-POLY1305 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 5CE953A1DE3 for <ipv6@ietf.org>; Thu, 8 Jul 2021 07:18:48 -0700 (PDT)
Received: from stereo.hq.phicoh.net (localhost [::ffff:127.0.0.1]) by stereo.hq.phicoh.net with esmtp (TLS version=TLSv1.2 cipher=ECDHE-RSA-CHACHA20-POLY1305) (Smail #158) id m1m1UrX-0000FWC; Thu, 8 Jul 2021 16:18:47 +0200
Message-Id: <m1m1UrX-0000FWC@stereo.hq.phicoh.net>
To: ipv6@ietf.org
Cc: Alexandre Petrescu <alexandre.petrescu@gmail.com>
Subject: Re: on-link and off-link addresses, side discussion
From: Philip Homburg <pch-ipv6-ietf-7@u-1.phicoh.com>
Sender: pch-b9D3CB0F5@u-1.phicoh.com
References: <162512790860.6559.14490468072475126698@ietfa.amsl.com> <CAFU7BAT0O9nsuhs5FyNjvPfRKY+EM1fLYKaMYTwaPg2QjZAEpA@mail.gmail.com> <61e14cd7-ff37-5380-e547-8a9b6d3993da@gmail.com> <CAFU7BASF-vas+PP2dVNXuqScQArC+joB-fwRGzG3UZnsqq1QJg@mail.gmail.com> <2f1f68a1-8130-45b6-0586-6340f5e0bf9a@gmail.com> <8FC82801-F5FC-4FC3-8946-C37D1420248D@thehobsons.co.uk> <6b51c620-af53-5171-7856-b39471907460@gmail.com>
In-reply-to: Your message of "Thu, 8 Jul 2021 12:19:54 +0200 ." <6b51c620-af53-5171-7856-b39471907460@gmail.com>
Date: Thu, 08 Jul 2021 16:18:47 +0200
Archived-At: <https://mailarchive.ietf.org/arch/msg/ipv6/kGjULbNr06RWRpXNArzp3T28dXw>
X-BeenThere: ipv6@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "IPv6 Maintenance Working Group \(6man\)" <ipv6.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/ipv6>, <mailto:ipv6-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/ipv6/>
List-Post: <mailto:ipv6@ietf.org>
List-Help: <mailto:ipv6-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ipv6>, <mailto:ipv6-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 08 Jul 2021 14:18:57 -0000
> Further, the definition says that "a node considers an address to > be on-link it is covered by a particular prefix". That operation, > 'being covered by', is not specified. > > One might think of the use of a longest prefiix match algorithm. > > A longest prefix match algorithm is defined in that RFC to be used > to determine which prefix (from a set of prefixes) 'covers' an > address. > > On another hand, the definition of 'on-link' says it wants to > identify whether a _particular_ prefix 'covers' an address (not to > try to identify whether an address matches better one prefix or > another). That is a distinct algorithm from the longest prefix > match algorithm. > > To give an example: by using a longest-prefix-match algorithm in > a normal way (identify which prefix out of a set of prefixes matches > better one particular address) one will always 'cover' an address > with almost any prefix. All allocated prefixes start with this > '000' triple bits. So they all cover any address; but in that > 'cover' operation one specifically adds that it covers up to 3 > bits. The 'cover' operation is successful, but just up to 3. I'm confused about what you are trying to say. The way I understand it is as follows: An RA may contain a prefix that has the onlink bit set. The interface is implicitly defined as the interface over which the RA arrives at the host, so there is no need to make this explicit. Information in an RA only applies to the interface over which the RA arrives. Then 'covered by the prefix'. Covered by the prefix 2001:db8::/80 means that if the first 80 bits of an address are the same as the first 80 bits of the prefix, then the address is said to be covered by the prefix. For onlink, there is no 64-bit boundary. Any prefix length should work. The prefix length determines how many bits are compared to decide on a match. Then, in theory there could be overlapping prefixes, some might be onlink, some might be not onlink. So in theory we could define a longest matching rule. However, this leads to code complexity and there don't seem to be any practical use cases for overlapping prefixes, so leaving this undefined and assuming that routers do not generate RAs with overlapping prefixes seems fine.
- Robert Wilton's No Objection on draft-ietf-6man-g… Robert Wilton via Datatracker
- Re: Robert Wilton's No Objection on draft-ietf-6m… Jen Linkova
- RE: Robert Wilton's No Objection on draft-ietf-6m… Rob Wilton (rwilton)
- Re: Robert Wilton's No Objection on draft-ietf-6m… Alexandre Petrescu
- Re: Robert Wilton's No Objection on draft-ietf-6m… Jen Linkova
- on-link and off-link addresses, side discussion Alexandre Petrescu
- Re: on-link and off-link addresses, side discussi… Simon Hobson
- Re: on-link and off-link addresses, side discussi… Alexandre Petrescu
- Re: on-link and off-link addresses, side discussi… Philip Homburg
- Re: on-link and off-link addresses, side discussi… Simon Hobson
- Re: Robert Wilton's No Objection on draft-ietf-6m… Wes Beebee (wbeebee)
- Re: why "is /64 [a] "default" prefix length when … Alexandre Petrescu
- Re: on-link and off-link Alexandre Petrescu
- Re: on-link and off-link Philip Homburg
- RE: on-link and off-link Vasilenko Eduard
- RE: on-link and off-link Pascal Thubert (pthubert)
- RE: on-link and off-link Vasilenko Eduard
- RE: on-link and off-link Pascal Thubert (pthubert)
- Re: why "is /64 [a] "default" prefix length when … Wes Beebee (wbeebee)
- Re: on-link and off-link Wes Beebee (wbeebee)
- RE: on-link and off-link Vasilenko Eduard