Hello Toerless
I'm not the right person to discuss this, one needs to be close to hardware
implementation to wee what's easy what's not. Still I'm curious what you have
in mind.
The backward-compatible piece is the core thing isn't it?
SRv6 flies over a legacy IPv6 network between SR-capable nodes. I believe it is
quite a selling point.
Do you intend to make addresses larger than 128bits and then encode network
programming in there?
If so, and speaking of 40 years-old networking, I'd be tempted to encode the
program as an address extension as opposed to within the address, and to leave
the address as is - like good old phone number extension. Arguably one could
define a SRH that is composed of {address_extension, next_address} where the
extension applies to the previous address (the destination in the IP header for
the first entry in the SRH.
For shorter-than-128bits addresses in a limited domain like an IoT network, yes
we've done quite a bit in the IoT space, with a degree of freedom that 6MAN
seems exempt. SCHC could give you almost anything you want, provided that you
can configure the right state everywhere. 6LoWPAN can exclude a well-known
prefix from the packet on the wire so you can have shorter local addresses.
What the IoT art does not give you is network programmability.
Keep safe;
Pascal
> -----Original Message-----
> From: Toerless Eckert <[email protected]>
> Sent: jeudi 8 avril 2021 2:24
> To: Pascal Thubert (pthubert) <[email protected]>
> Cc: Stewart Bryant <[email protected]>; Brian E Carpenter
> <[email protected]>; draft-jia-flex-ip-address-
> [email protected]; int-area <[email protected]>; Jiayihao
> <[email protected]>; draft-jia-scenarios-flexible-address-
> [email protected]
> Subject: Re: [Int-area] Using ISO8473 as a network layer to carry flexible
> addresses
>
> Pascal,
>
> Yes, the low-power world in IETF invented a lot of concepts that SRv6 then
> reinvented, but heck, late in the process they managed to at least
> acknowledge some of that prior work through references ;-) nd not, the
> logic around compact alternatives to SRH also started with the premise
> that those shorter representations are compressed versions of IPv6
> addresses (if i still understand it right).
>
> This is all great and fine if we think that the only future we can think
> if is one where we try to fit everything we want to innovate on into the
> tight box of rfc8200. And while i agree tht there may be good short-term
> reasons for such options, i just don't see this as a viable long-term
> option to significantly evolve our network layer protocol benefits beyond
> the original esign of 40 years ago. At least not without incurring a lot
> of technology dept that makes it more and more difficult to deploy and
> expand with.
>
> To me the much more interesting question to ask than "how can we make
> innovation fit rfc8200"
> is how we could provide the most backward compatible superset of network
> layer functionality that does allow us to carry forward what we need
> (e.g.: IPv4/IPv6 semantic), but also allows us to extend semantics
> (especially addressing) in the most cost-effective/performance/least-
> obfuscated way.
> And i don't think it is hard.
>
> The mayor stumbling block IMHO is to recognize that unlike maybe 25 years
> ago when
> ISO8473 was around, we nowadays IMHO do NOT have any issues high-speed
> hardware forwarding anymore to have headers with different length address,
> but using a unified forwarding plane logic and hopefully even much more
> shared control plane as eventoday acros IPv4 and IPv6.
>
> If we just had those variable length adddresses, all the discussions about
> SRH alternatives would go away because each address element could have a
> forwarding component as short/long as necessary for the network and as
> many programmabiliy bits behind it as desired - for this element.
> Likewise, i would venture to guess that a lot of the low-power network
> solutions would become much simpler and efficient by aleviating the need
> to compress addresses.
>
> Cheers
> Toerless
>
> On Wed, Mar 03, 2021 at 11:05:42AM +0000, Pascal Thubert (pthubert) wrote:
> > Hello Stewart, Brian and Toerless:
> >
> > Interestingly RFC 8138 took one step in that direction. Yes you???re
> going to need a new Ethertype but it???s still IPv6 I. That is is
> expressed as a compression not a modification of IPv6.
> >
> > In the compressed form the header starts with the next hops, the
> destination and SRH being indiscriminated, the destination is just the
> first of the list. The size is variable but each hop is at most 128 bits.
> Because the SRH could encode SRv6 you can already go a long way with this.
> >
> > If that can help you do what you want, I m happy to explain more...
> >
> > Keep safe.
> >
> > Pascal
> >
> > Le 2 mars 2021 à 13:33, Stewart Bryant <[email protected]> a
> écrit :
> >
> > ???
> >
> > On 1 Mar 2021, at 20:08, Brian E Carpenter
> <[email protected]<mailto:[email protected]>> wrote:
> >
> >
> > It would take but a minute to design a longer-address mechanism for
> IPv6, although I don't have space to include it in the margin of this
> email**. But it would take many years for it to be widely implemented and
> deployed, during which time the Internet would be opaque to such
> addresses.
> >
> >
> > ** Basically, use a prefix such as fb00::/8 to indicate an extended
> address.
> >
> > Hi Brian
> >
> > Basically I think that this fails the backwards compatibility text.
> >
> > It is perfectly legitimate to write an IPv6 forwarder as follows:
> >
> > If MACaddress == me and MACtype == IPv6 pass packet to IPv6 forwarder
> >
> > In IPv6 forwarder:
> >
> > If version == IPv6 and Hop Limit not exceeded send bytes 24 to 39 to
> > address lookup engine
> >
> > Wait for address result and forward packet accordingly
> >
> > Except that this forwarder would have sent a bunch of random junk to the
> ALE consisting of some of the SA and maybe some of the DA depending on
> their sizes.
> >
> > So to stop an old and legitimately designed parser being fooled you
> really have to use a new MAC type and a new version and as soon as you do
> that you might as well design the packet optimally for the job at hand.
> >
> > If the IPv6 designers had followed the strategy of both the Ethernet
> designers and the ISO8473 designers and put DA before SA then the elegant
> approach that you and others have proposed at various times would have
> worked nicely.
> >
> > Best regards
> >
> > Stewart
> >
> >
> >
> >
> > _______________________________________________
> > Int-area mailing list
> > [email protected]
> > https://www.ietf.org/mailman/listinfo/int-area
>
> --
> ---
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