On 04/02/2022 16:08, Templin (US), Fred L wrote:
Gorry, thanks and see also below: Fred-----Original Message----- From: last-call [mailto:last-call-bounces@xxxxxxxx] On Behalf Of Gorry Fairhurst Sent: Friday, February 04, 2022 4:36 AM To: touch@xxxxxxxxxxxxxx; Tom Herbert <tom@xxxxxxxxxxxxxxx> Cc: draft-ietf-6man-mtu-option@xxxxxxxx; ipv6@xxxxxxxx; last-call@xxxxxxxx; Templin (US), Fred L <Fred.L.Templin@xxxxxxxxxx>; IETF- Announce <ietf-announce@xxxxxxxx>; 6man-chairs@xxxxxxxx Subject: Re: [Last-Call] [EXTERNAL] Re: Last Call: <draft-ietf-6man-mtu-option-12.txt> (IPv6 Minimum Path MTU Hop-by-Hop Option) to Experimental RFC EXT email: be mindful of links/attachments. See below at bottom. On 04/02/2022 02:13, touch@xxxxxxxxxxxxxx wrote:Sure - that works. I’m just hoping we don’t create something so future-proofed that it is present-prevented. Joe — Joe Touch, temporal epistemologist www.strayalpha.com <http://www.strayalpha.com>On Feb 3, 2022, at 3:37 PM, Tom Herbert <tom@xxxxxxxxxxxxxxx> wrote: On Thu, Feb 3, 2022 at 3:16 PM touch@xxxxxxxxxxxxxx <touch@xxxxxxxxxxxxxx> wrote:Fair enough. Two more bytes burned for largely no reason for the foreseeable future, but so be it.Joe, It's more like eight more bytes burned since both two byte fields need to be extended to four bytes and the EH needs to be padded to have length in units of eight bytes. Given that MTU's that exceed 64K are exceedingly rare, this does seem like a lot of overhead to add to potentially every packet. Also, if the sender already knows that its local MTU is less than 64K, the discovery that the network supports a higher MTU doesn't seem to be useful information. An alternative might be to define a long format of the option with larger MTU fields that can coexist with the already defined option. This could be done by using the same option type number, but discriminating between to the two formats based on the option length. Tom— Joe Touch, temporal epistemologist www.strayalpha.com <http://www.strayalpha.com> On Feb 3, 2022, at 2:13 PM, Templin (US), Fred L <Fred.L.Templin@xxxxxxxxxx> wrote: Hi Joe,Why stop at 32 bits? They COULD expand to 128. Or 1024. Or more.RFC4443 PTB stops at 32 bits and RFC2675 Jumbo Payload stops at 32bits. So should this.If and when we ever get close to 64K, we could easily declare all 1’s as indicating the need for an extended valueIP parcels give a reason for link MTUs > 64K, and link designers will start to take note.IMO, let’s not complicate things unnecessarily now.I understand, but the problem is this document is reserving one of the few scarce HBH option codes still available. And, once locked in at whatever MTU field size we agree on it will be impossible to change in the future. It is not complicated to make the field sizes 32bits now, which would match RFCs 2675 and 4443. Fred From: ipv6 [mailto:ipv6-bounces@xxxxxxxx] On Behalf Of touch@xxxxxxxxxxxxxx Sent: Thursday, February 03, 2022 1:47 PM To: last-call@xxxxxxxx Cc: draft-ietf-6man-mtu-option@xxxxxxxx; ipv6@xxxxxxxx; IETF-Announce <ietf-announce@xxxxxxxx>; 6man-chairs@xxxxxxxx Subject: [EXTERNAL] Re: [Last-Call] Last Call: <draft-ietf-6man-mtu-option-12.txt> (IPv6 Minimum Path MTU Hop-by-Hop Option) to Experimental RFC Why stop at 32 bits? They COULD expand to 128. Or 1024. Or more. Right now, anything above 1500 is a unicorn outside closed environments (e.g., data centers): https://tma.ifip.org/2018/wp-content/uploads/sites/3/2018/06/tma2018_paper57.pdf A lot of the point of this option is to figure out what number below 1500 works - and/or when numbers even below those required for IPv6 minimums are needed. If and when we ever get close to 64K, we could easily declare all 1’s as indicating the need for an extended value. IMO, let’s not complicate things unnecessarily now. Joe — Joe Touch, temporal epistemologist www.strayalpha.com On Feb 3, 2022, at 1:16 PM, Templin (US), Fred L <Fred.L.Templin@xxxxxxxxxx> wrote: I have a comment - section 5 ("IPv6 Minimum Path MTU Hop-by-Hop Option") sets aside two 16-bit fields to record MTU values. This places an upper bound limit of (2**16 - 1) octets on the MTU that can be recorded at each hop, but this will be too small for IP parcels which can grow to (64 * (2**16 -1)) octets. And, if support for true jumbos may be needed in the future the fields should probably permit sizes up to (2**32 -1) octets which would require 32-bit fields. Fred -----Original Message----- From: ipv6 [mailto:ipv6-bounces@xxxxxxxx] On Behalf Of The IESG Sent: Thursday, January 27, 2022 4:38 PM To: IETF-Announce <ietf-announce@xxxxxxxx> Cc: draft-ietf-6man-mtu-option@xxxxxxxx; ipv6@xxxxxxxx; 6man-chairs@xxxxxxxx Subject: Last Call: <draft-ietf-6man-mtu-option-12.txt> (IPv6 Minimum Path MTU Hop-by-Hop Option) to Experimental RFC EXT email: be mindful of links/attachments. The IESG has received a request from the IPv6 Maintenance WG (6man) to consider the following document: - 'IPv6 Minimum Path MTU Hop-by-Hop Option' <draft-ietf-6man-mtu-option-12.txt> as Experimental RFC The IESG plans to make a decision in the next few weeks, and solicits final comments on this action. Please send substantive comments to the last-call@xxxxxxxx mailing lists by 2022-02-10. Exceptionally, comments may be sent to iesg@xxxxxxxx instead. In either case, please retain the beginning of the Subject line to allow automated sorting. Abstract This document specifies a new IPv6 Hop-by-Hop option that is used to record the minimum Path MTU along the forward path between a source host to a destination host. The recorded value can then be communicated back to the source using the return Path MTU field in the option. The file can be obtained via https://datatracker.ietf.org/doc/draft-ietf-6man-mtu-option/ The following IPR Declarations may be related to this I-D: https://datatracker.ietf.org/ipr/4567/ -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@xxxxxxxx Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 -------------------------------------------------------------------- -- last-call mailing list last-call@xxxxxxxx https://www.ietf.org/mailman/listinfo/last-call -- last-call mailing list last-call@xxxxxxxx https://www.ietf.org/mailman/listinfo/last-call -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@xxxxxxxx Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 ---------------------------------------------------------------------- last-call mailing list last-call@xxxxxxxx https://www.ietf.org/mailman/listinfo/last-callThanks for asking this: I'm going to push back a little on extending the method to future-proof it... The motivation for an HBH option is to help support equipment that indeed wishes to deploy a larger MTU, targeting jumbo Ethernet frames. Personally: I 'm not convinced we should add to this spec to provdie extensibility for future experiments with new IP link technologies supporting greater than 64KB. I'll argue for the target purpose a fixed sized HBH option is more deployable, and likely to be useful for the "foreseeable" future. If it helps, we could add text saying a host wishing to use a MTU larger than 64KB must not use this HBH option, although that might be obvious.I think what is being asked is very simple and not hard at all to implement. It is just a simple test of the option length - if the length is 4 the option is in "short form", and if the length is 8 the option is in "long form". But, the overriding consideration is that there is an impending use of Jumbos that we believe will begin to emerge in the near term called: "IP Parcels". If you have not heard about them yet, I strongly suggest you have a quick look: https://datatracker.ietf.org/doc/draft-templin-intarea-parcels/ IP Parcels should become an early adopter of your MTU option, but they can be larger than 64K (up to 4M) and would very soon want to begin using the long form. Plus, the MTU option would only be used on path qualification messages and not on every single packet so using the long form would not introduce any unnecessary inefficiencies. So yes - please include both long and short forms of the MTU option in the first publication - because it is very likely going to cast the option in stone for the forseeable future. Thanks - FredGorry -- last-call mailing list last-call@xxxxxxxx https://www.ietf.org/mailman/listinfo/last-call
I did read the draft you pointed to thanks, because I anticipated that your query might be linked to this topic - my thought is that if your work was to proceed in future at the IETF, then you might be able to take advantage of the HBH option proposed in the draft for traversing standard links (i.e. with KB of MTU).
If your thought was to use packets and frames larger than 64 KB, then there would be many issues to consider. There are various possibilities including a new header that might be the best way forward for those paths that wish to support this approach - I'd expect you'd need new functionality anyway at routers to handle this change in architecture. This was not what was considered in draft-ietf-6man-mtu-option.
Gorry -- last-call mailing list last-call@xxxxxxxx https://www.ietf.org/mailman/listinfo/last-call
