Re: why "is /64 [a] "default" prefix length when a length isn't specified."
Alexandre Petrescu <alexandre.petrescu@gmail.com> Mon, 12 July 2021 13:28 UTC
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Subject: Re: why "is /64 [a] "default" prefix length when a length isn't specified."
To: "Wes Beebee (wbeebee)" <wbeebee@cisco.com>, Jen Linkova <furry13@gmail.com>
Cc: 6man <ipv6@ietf.org>
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> <6A22DCF6-5132-44D3-AB45-E9C151376D2C@cisco.com>
From: Alexandre Petrescu <alexandre.petrescu@gmail.com>
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Date: Mon, 12 Jul 2021 15:28:44 +0200
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Tell me, why 64 is a default in the eyes of an impplementer when a length isn't specified? Alex Le 12/07/2021 à 15:18, Wes Beebee (wbeebee) a écrit : > For a more complete discussion of on/off-link, please refer to "IPv6 Subnet Model: The Relationship between Links and Subnet Prefixes", RFC 5942. > https://datatracker.ietf.org/doc/html/rfc5942 > > - Wes > > On 7/1/21, 6:47 PM, "ipv6 on behalf of Jen Linkova" <ipv6-bounces@ietf.org on behalf of furry13@gmail.com> wrote: > > On Fri, Jul 2, 2021 at 12:05 AM Alexandre Petrescu > <alexandre.petrescu@gmail.com> wrote: > > Aside from the conversation above that I agree with, and aside of the > > fact that I agree that RFC 4861 does define the term "off-link" too by > > opposing it to a better defined "on-link" term, I must say that I never > > used or heard in practice people talking about off-link or on-link > > addresses. > > Well...I guess our experiences vary significantly. I hear those terms > a lot and I do use them all the time. > > > If one wants to talk about off-link or on-link addresses then one talks > > about neighbors or not neighbors. > > Well, strictly speaking, neighbor is a *node* attached to the same > link. Being on-link or off-link is a property (of an address, for > example). > > > We around me usually talk casually about link-local addresses (adresses > > 'lien', fr.), but we never talk about off-link or on-link addresses. > > I find the on-link/off-link terms very useful because in my work I > have to distinguish between "communication with neighbors" and > :communication with the rest of the network, via routers". > Terms like "intra-VLAN"/"inter-VLAN" are too topology-specific etc. > > > Then, there is the use of the term 'on-link' in RFC4861 which is at > > times glued to 'prefixes', even though it is formally defined to mean > > 'addresses'. > > For example, a full expansion of this RFC4861 text: > > "These options specify the prefixes that are on-link" > > would actually mean > > "These options specify the prefixes that are on-link, i.e. addresses > > assigned to an interface on a specified link" > > which is somehow difficult to understand. > > > > The most confusing is probably the expansion of this text: > > "L 1-bit on-link flag." > > which, when expanded, it would mean > > "L 1-bit on-link addresses flag" > > when it is, in fact, a flag about prefixes in PIOs, and not about > > addresses. These prefixes are often used for other operations than just > > forming addresses. It is thus difficult to grasp. > > I suggest you look at it from a different angle. > "on-link address" is defined as an address that is assigned to an > interface on a specified link. > There are different ways to indicate that the address is on-link and > one of them is "the address is covered by an on-link prefix, e,g, as > indicated by the on-link flag in the Prefix Information option". > L bit just indicates that addresses covered by the prefix shall be > considered on-link. That's it. > > > This 'on-link' and 'off-link' discussion relates a lot to the > > difficulties we have in suggesting at IETF that a new extension is > > needed to tell that a prefix advertised on a link might not be for that > > link to be used for SLAAC, but for putting in a routing table entry. A > > little bit similar to RFC4191's RIOs. > > OK, disclaimer: I'm writing this before my first coffee...but...L flag > has nothing to do with SLAAC, A flag is used for that. > L=1, A=0 would just mean 'addresses on that prefix are on-link but do > not use the prefix for auto-configuration'. > > Smth like: > > 2001:db8:1::/64----node1-------node2 > If node2 receives a PIO for 2001:db8:1::/64 with L=1, A=0 it would > assume that 2001:db8:1::f00, for example, is on-link and would try to > resolve its link-layer address using ND. > If node1 acts as an ND proxy, it would work. > > > But when told that the RIO of RFC4191 might be appropriate for the V2V > > case that I needed I always reply that what we need is an RIO that is > > always outside the link (I dont use the term 'off-link'), and always at > > least 2-hops away, never 1-hop away. SO there I dont use either the > > on/off-link terms. > > Sorry, I've not been following that discussion. Wouldn't "L=1, A=0 + > ND proxy" do what you want? > > -- > SY, Jen Linkova aka Furry > > -------------------------------------------------------------------- > IETF IPv6 working group mailing list > ipv6@ietf.org > Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 > -------------------------------------------------------------------- >
- 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