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 value > >>> > >>> IP 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-call > > > Thanks 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 - Fred > Gorry > > > > > -- > 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
